So I have been playing Muslim quite religiously since Sword of Islam was released, and I have become quite proficient with the 'min-maxing' strategy as it applies to this game. I can't help myself, I just have to play this way. I will uncover and abuse any game mechanic I can in order to 'win' as efficiently as possible. I do not cheat, and I HATE cheating, but if it can be done 'fairly' in this game then I do it.
So here are a few balancing problems I've found that I think need to be addressed:
1) The penalty for breaking truces is too small. If you are going to obliterate a small religious group, the penalty for doing so is nearly non-existent. The initial prestige penalty of 100 is offset by the victory prestige, meaning you simply don't gain as much prestige for the war. The relations penalty doesn't matter for a couple reasons, #1 its only for the nearly exterimated religion, #2 because it only applies to your current ruler. So you could obliterate the world, and your heir then has all this land with no penalty.
2) Muslims have too easy of a time generating relationship bonuses. +20 relations with ALL MUSLIMS is only 500 piety. This is easy to attain, and on top of the +20 you can get from having 2k prestige, you have a near perfect relationship with your entire realm. This is probably why they seem to have such large levies compared to the christians. On top of these, you also get +10 for Hajjaji or however its called, and if you are playing as Shia you get the +10 for being a descendant of muhammid.
3) The 'penalty' for taking fewer wives is a joke. -3 per month and you can simply play with 1 wife. Then you have no challenges with succession, and very few challenges with decadence. The decadence system ends up being a permanent bonus to your income and moral. You can play with a low county count, like 1-3, and the reduction to decadence is huge. Instead of landing your children, you simply appoint them as advisors, and they have -.4/mo from that alone. My point is, you never have to land your children and you can still maintain 0 decadence. On top of that, you essentially have elective succession because you control who your heir will be by having him gain some land. This again fuels the problem listed in #2, because you pick the perfect heir that has perks everyone will like, like patient, genius, strong, kind.
4) The invasion CB needs to be reworked. As it works now, you spend 500 piety to attack anyone that isn't EXACTLY the same religion you are, and upon victory instead of a typical holy war state (which I would argue this is just a larger version of a holy war) , all of the counties not directly held by the former king are 'subjugated'. They stay held by the current owner, and you are given a +75 relations BONUS with them. Now this is where muslim really gets broken: You use the relationship bonuses listed in #2 and #3, and you simply revoke all of the christian titles. Since they are infidels you can do it for free, since they have +75+20+20+10+10+X relations with you, even though you are a foreigner and an infidel to them, they will accept the revocation outright. If they won't, send them a gift and then revoke. If they still won't, who cares, revoke anyway, smash the rebellion and then revoke the title again! Heres the problem: After you revoke the title, you can give it to a muslim of your culture, and the your new land is run by people who like you, and there are no "recently conquered" maluses. Since originally the former owner maintained his land and it was not taken via war, much the same as a de-jure territory war, he doesn't get these penalties. Since you are 'revoking' the title, not waring for it, you don't get the penalties either. Using this tactic you can subjugate huge areas of the world, revoke their titles, and you have a stable realm where you draw levies and income.
5) Mercenaries should count as raised levies for the requirement before declaring a war. You shouldn't be able to park men in someones county, then declare war. Thats why you can't do it with your own armies, and I don't see why you should be able to do it with mercenaries. The AI doesn't do it, don't allow the player to do it.
Those are the primary issues I've seen, as for suggestions:
1) Make truces unbreakable, or make the penalty so significant that it must be honored outside of extreme circumstances. An idea would be to give your character/family a trait 'Truce Breaker', which gives a permanent -10 relations with EVERYONE for the life of your current character, and maybe your heir gets -5 for being the descendant of a truce breaker. After the 2nd generation, it fades.
2) Nerf the piety relations bonus, either be increasing the amount of necessary piety to max the bonus (is 500 up to 1000), or simply reduce the max relationship bonus from 20 to 10. The Hajjaji bonus seems silly to me, if every muslim does it, why does it make others like you? I'd rather see that bonus down from 10 to 5, or perhaps instead of a bonus at all, give you a penalty of -10/5 if you DON"T go on the hajj to mecca. That would seem more appropriate to me, since everyone goes you would be the pariah by not having done it.
3) Have events pop up that force you to wed, like an ultimatum based on your rank. IE "You must wed this random courtier, or suffer -200 prestige". Something must be done to make this more of a requirement. Having multiple wives, and more importantly having half-brothers, is an integral part of the decadence system. Right now its too easy to manipulate.
4) I don't understand why the invasion CB causes subjugation instead of the same outcome as normal holy wars. When you go on a crusade for Jerusalem, the outcome is that all that territory is ruined for 30 years. When you go on a jihad, same thing. Why is the invasion cb different? Its broken. I think that if you win this war, the county level penalties should apply. Or at the very least, if you revoke a christian held territory as a muslim, if it is a religion-sponsored revocation (Is 'since he is a filthy catholic, no one will care), then you should get those penalties. If you have a claim, or the person is a traitor, perhaps the penalties shouldn't happen. But the mechanic feels broken right now. I have conquered all of the byzantine and holy roman empire, ireland, scotland, england, france, denmark, norway, poland, hungary, the cumans in 30 years. I project world obliteration within 60 years total. This isn't right!
5) Just change the requirement so players can't abuse the AI.
In closing, these are my observations and suggestions, I would like to hear what your ideas are, if you agree with me, if you think the suggestions are a good solution, or if you disagree. I just want to see some ideas! Hope you enjoyed the read.