While I really enjoy PvP in this game, I find it too much of a "rock paper scissors" game, and don't like the fact that most spell combinations are pretty useless. Additionally, there are some items that are way better than others, and select few magicks that are way better than all the other relatively-crappy ones.
As most of us know, there are currently some spells that are simply way better than any similar variation of the. Giving some select examples:
Ice Wall of Death
Ice wall of death (Ice+cold+shield+lightning+arcane), mostly used on a weapon, is the probably the most powerful short to mid-range damage dealer in the game. While easily defended with the appropriate elemental shield, I find it rather silly that when the opponent is not using that shield, and is in range, there is no better spell to use. Both lightning shocks and arcane explosions are way too powerful. Lightning wall elements should probably consumed once they shock (and possibly have their damage adjusted so that they don't become useless), and arcane wall explosions need to deal a bit less damage.
Ice sword is again a short to mid-range 1-shotter if the enemy is not defending with rock/ice armor.
Giving it 1/2-physical 1/2-cold damage would mean it becomes survive-able if you have either cold or rock shield up, but not be perfectly countered by either.
Rock shields and shields that protect against arcane+lighting+whatever are also way too hard to counter (basically you must counter the elemental shield with ice sword and counter the rock shield with ice wall of death, though rocks obviously also work, tough I'll get to discussing rocks later as they are a more complicated problem). More importantly than how hard they are to counter - There is simply no reason to use any other shield. Refreshing is fast enough, aura radius is meaningless, and adding more elements is free as long as you're fast enough and aren't adding the same element twice.
Multi-element shields should probably just have reduced effectiveness by not providing full immunity. For example, a fire shield could give 100% fire resistance, but fire+lightning shield would give only 80% resistance to both, while fire+lightning+arcane shield would only give 70% resistance to all 3. Conjuring multiples of the same element for the shield would reduce the penalty, but not eliminate it, so for example 3 fire 1 lighting shield would give 95% fire resistance but only 80% lightning resistance. Of course those numbers are just examples and can be messed with for best balance.
Rock/ice shields should only defend against physical damage, but can be mixed with any other element (though, of course, cut the resistance down like any other mixed elemental shield). Currently mixing non-fire/cold elements doesn't seem to do anything, while mixing a single fire/cold element gives protection to that element for unlimited duration, making you vulnerable only to the other element and overpowered spells. Possibly slightly buff the shield to compensate, though I'm not sure if it's even necessary. Maybe just slightly reduce the movement speed penalty.
Element Mixing VS Stacking
Mixing elements is encouraged too strongly. Currently there are 2 primary game mechanics that encourage it, and I think both could use some adjusting:
1. Spell effectiveness:
Charging the same element on a spell isn't nearly as good as mixing. While in principal this is a good mechanic, it is greatly overdone for some spells. For example, ice sword, ice AOE and rock shield seem to have reasonable scaling with more of the same element, while healing (at least the self version) doesn't scale at all, and some spells only scale in radius and not damage. There are a lot of spells that need to have this aspect adjusted, so I'll list a few examples.
Fire/Arcane/Cold ball and fire/cold sprays: They (or at least the balls) seem to only scale in range. While this is good, some small damage increase would be a good idea. This is on top of sprays starting at way too short of a range and maxing out a bit too short too. Charging up more rocks doesn't seem to do anything - it should increase the damage! Rocks should increase damage more than the element itself, since they don't increase the AOE, but still not be a very large increase. Additionally, ball spells could actually get some small direct impact damage that would be increased by adding more rock elements (please correct me if this exists already, as I haven't noticed it but also haven't thoroughly tested it). Of course mixing elements here gives a direct damage addition, making them much much stronger than any single element variation, and overall deal too much damage (especially that steam+arcane ball).
Self healing not scaling makes no sense. Charging up multiple life elements puts you at a greater risk, and should reward you with a bigger heal! In the end (after all balance changes), stacking life up to 5 and then healing should provide more HP per second than just casting heal with 1 life element multiple times, to compensate for the extra risk you need to take in order to use the 5 life element heal.
Elemental shields scaling in duration and radius would be interesting if mixing different elements in a shield would receive appropriate nerfing. Currently doubling up on the same element is completely useless because you could instead just make yourself immune to yet another element. One possible idea is making a single-element shield heal you rather than just protect you, but for a small percentage. For mixed shields I already gave an example for how charging up on the same element twice can be made useful (reduce mixing penalty).
2. Conjuration speed:
Conjuring any additional element takes 0 time, while there is actually a delay for charging up on the same element! While I do think it's cool that the point of the game is to create cool mixes, this combined with #1 goes overboard, completely blowing any idea of using a single element out of the water. If conjuring elements would always grant a delay, then mixed spells might still sometimes be more powerful, but not nearly as much. In fact, conjuring is already pretty fast even with the delay, and could slightly be slowed down (perhaps made 1.2~1.5x slower), to make the game a bit more tactical and a bit less about speed. In any case, applying the same single-element delay to multiple elements will make the player have to think whether he actually wants to conjure a 5 element spell, or maybe just go along with 1-2 elements and fire it up. With some adjustments to casting and casting speed mechanics, this could still keep multiple-element spells very useful.
Conjuration and Casting Mechanics (spamming)
The last point leads me to talk about the spamming issue. Currently, you can actually start conjuring your next spell while still playing the casting animation of the last one! This is especially bad with fast cast spells, mostly ball spells but also AOE spells. It makes the game very dependent on your ability to spam rather than your ability to pick the right spells at the right time and aim them properly, and encourages you to use spells that are quick to conjure (currently mostly arcane+steam ball and its friends, with some occasional ice AOE).
Slowing down the casting animation for the problematic spell types and delaying element conjuration can both prevent spamming, slow down the game a little, and if done properly also encourage using complicated spells when you can afford it but using simple spells when you simply must cast a spell *right now*.
To make things more user-friendly, trying to conjure elements "too fast" should "queue" the next element to be conjured as soon as the game allows it to, and give some sort of minor visual sign (anything will do) when all elements have been conjured, and if possible, also show what elements are going to be conjured. For exmaple, if I quickly click 5 water and 5 cold elements, I will see 1 water element normally, then next to it 4 faded water elements and next to them 5 faded cold elements. As the delay passes, more of the "queued" elemenets will become unfaded as they are conjured. Trying to cast any spell while conjuring will simply cast it with whatever have been conjured so far, ignoring and erasing the rest of the queue. That way you will not have to actually conjure elements in any specific rhythm even though there is a delay.
Slowing down conjuration speed will also fix some problems with the magicks, but not completely, which leads me to the next topic.
Some are completely useless, at least against players, while few are powerful on a game-changing level. I like having magicks giving extra flavour to the game, but I don't like them being spammed or never used at all. Some magicks will be automatically balanced by introducing the delay for conjuring different elements, but not all of them.
All "global" magicks (ex: rain, time warp) seem rather useless in PvP, since they hurt you just as much as the other guy (who can shield against them just like you). Not sure how to adjust those since the problem is in their concept.
Some are simply not very useful even though their concept is cool, such as grease, phoenix, summon death or vortex. They need to be adjusted, so that they are more easily used in a way that will actually benefit you against the opponent. Again, not too sure how to actually improve them, though making summon death less luck-based is a good start.
Some are extremely powerful, specifically haste, thunder bolt and fear. Summons (for magicks that would be elementals and zombies) can be extremely annoying to deal with.
Haste: Reduce speed and duration. Possibly increase the duration of the casting animation slightly.
Thunder bolt: While its main overpowered part is the damage, if it dealt less damage it would become useless. Instead, it would probably be best to simply slow down its casting animation (combined with not being able to conjure elements while the casting animation is playing, making it much less spam-able and easier to defend against with an appropriate shield). It should be slow enough to give you time to cast a lightning shield with at least half a second to spare for reaction time. Maybe even give it a more unique animation. It also shouldn't knockdown "heavy" targets.
Fear: Reduce duration, and probably range as well.
I might have missed some magicks that I have less experience with, but I hope the general idea is clear.
Weapons and Staves
Some weapons simply deal terrible damage. Damage and attack speed of such weapons should be increased! I have not yet experienced with all weapons, so I can't really make a list of all the overpowered/underpowered ones, but I know enough to tell they need some major balancing. Especially the firearms, with weapons like the RPD and M60 being monsters, and M16 being a pretty evil killer itself. And don't even get me started about that RPG, which really needs to reduce damage to 1800, reduce indirect damage even more, slightly increase reload time, and remove knockdown against heavy targets, and be changed to 1/2-fire 1/2-physical.
For staves there are obvious stuff like the double HP staff. I also don't really like the staves that have powerful effects on very long cooldowns. I find staves like the staff of liberty (with the grenades, though the AOE in which they kill in 1 shot might need some slight reduction), or epic staff (though I think its +damage should just be constant and not activated) much more interesting, and it would be nice if most staves would be brought to about the same power as those staves.
Some robes are just way too awesome! Stuff like decent physical resistance and increased HP are way too good compared to the life resistance or even immunity, or a weakness to some random element. Robes should have flavor, but not overpowerness. Epic robe's life resistance could work better to balance it if the healing ice wall nerfed (both through slowing down element conjuring and by mine/wall changes discussed later).
The vietman soldier robe is a nice example for a middle-of-the-road robe, where you get a nice firearm and staff but no cool attributes.
Rogue robe is way too extreme on the vulnerability and the speed. A bit more HP and less speed would make it more interesting.
Robe and Hat, Patched Robe and Vanilla robe really need some more usefullness.
Overall there's way too much imbalance in the robes department to really write down what needs to be fixed. First the amount of variety needs to be set, then the attributes adjusted to fit into that standard.
Misc stuff that didn't fit anywhere else
Rock stalements - When one player casts a right-click shield and both players charge up a rock, the first to release the rock once the shield is down wins. If one didn't charge a rock in time, he must hide, and in some situations can never come out of hiding, resulting in a terrible stalement. Something needs to give you the ability to get to the player, such as being able to keep advancing by casting more shields forward and/or getting an ability to make him drop the rock through the shield by, say, using water spell (regardless of his weight, if he's heavy it won't knock him down but still make him drop the rock), or by allowing rock weapon imbues to go through shields and increase their 5-charge range (so that you can knock him down "through" the shield that prevents him from killing you, forcing him to release the rock). I personally like the last solution the best.
Mines are too powerful and dense. Damage needs tuning, and especially the AOE. It's currently almost impossible to only get hit by a single explosion.
Walls cast range/radius (with right-click cast or AOE cast) is too small. Arcane mines are almost close enough to hit you, and healing ice walls are close enough to heal you to way more than full HP. Spreading out the wall elements a bit more and increasing the radius will somewhat tune down all the extreme effects that wall can create, without making them useless (a single arcane explosion should still deal decent damage and knock up, and healing explosions should still do reasonable healing). Increasing range of right-click will also allow to slowly advance by casting a normal shield, advancing and then casting a new one, until you are in range to break the rock stalement with the suggested shield-penetrating rock weapon enchant.
Fire needs a bit of direct damage (or a bit more of it so that it is actually noticed), and a tiny bit less damage over time to compensate.
Cold needs to deal more damage. It should still be much lower damage than any other element, however currently it deals practically 0.
Spray spells (both on right-click and weapon cast), unless I'm missing something, are pretty useless. Cast on weapon should at least give some more noticeable burst of damage, and right-click channeling should be somewhat comparable in damage to beam spells, especially when you consider the spray spells have a much shorter range.
Overall, I think many of these balance changes will also positively affect single player and coop gameplay, though obviously there are probably many more changes that could be made to improve that experience (ex: Add more elements to revive to make it slower to use with the suggested slower element conjuration, make "new game +" noticeably harder, nerf some super-big AOE stuff).
There's probably much more, but if 1/2 of that will be taken into account by the developers I'll be one happy customer