Cutting down on micromanagement
If there is one thing that can be a killer in HOI it is not the bugs or the AI, because they will be fixed and upgraded, respectively, it is unnecessary micromanagement. So without any further ado, let's take a look at a few common issues and possible solutions.
Issue: Why does that damn scrolldown list of units keep resetting to the top, whenever I have made a change in the middle of the list?
Sheer perversity. If I'm changing something in the middle of the list, it is likely that my next action on the same list (if I have any further actions) will be in approximately the same place of the list rather on the top given how the list is sorted. Forcing the user to scroll down ten times to deploy ten divisions because he ordered some aircraft after the divisions entered the force pool, rather than maintaining the current focus of the list (allowing him to deploy the ten divisions without scrolling more than once) serves no good purpose for the user.
Solution: Maintain focus on the list
Issue: I just repaired 20 submarines from the same fleet (1 click to order) and have to click 60 times to return them to their fleet! (or 40 times to return them to the province they were sent to be repaired from.
A unit in the force pool has one button denoting the province it was removed from, which is used when tracking which provinces it can be placed in when deployed. Add a
new button to the right of this that deploys a unit to the province it was taken from. Let this button only be shown when the province is still controlled.
Yes, that's right. That just killed half the button clicks when repairing ships or upgrading armour.
One might even suggest a further small button (there is plenty of room on that line), that deploys a unit to the army/navy it came from where appliccable (formation still exists and is in a location this unit would be deployable to): This would allow you to return repaired and upgraded units to their formation with one click rather than two or three. Incredibly useful for those with many divisions.
Solution: Add buttons. (Ouch interface redesign, even relatively trivial, is never nice)
Issue: HOI didn't implement one of the hotly desired issues from EU1&2, namely the ability to actually order something done via the ledger
You can still use the ledger to get very good and useful information, and you still need to go and hunt down the correct army or province by hand afterwards. Where is the nifty round button by the province-lists denoting "zap to this province on the map" or on the army lists "zap to this army on the map"?
Why, as the USSR, do I need to check literally hundreds of provinces by hand on the map to see which I should upgrade, when the ledger has the ability to show all sorts of useful information? One of the most mind-numbing time-consuming actions is going thorugh all the provinces to see which you want to upgrade IC in, but the ledger already has the ability to sort your controlled provinces by IC. A little round button to begin upgrading IC next to a province on the list, or even just clicking on the IC entry for the province in the list would make this so much less time-consuming. List, sort by IC, lowest first, and click on those you want to upgrade. You could even use two different shades of gray in the list to distinguish between provinces currently upgrading and those not currently upgrading.
Issue: Strategic redeployment, time
A nasty issue and several possible solutions to the "Manchuria to Austria" in three days solution have already been proposed. Perhaps, as awful as it would be, I'd actually have to encourage more micromanagement by suggesting a maximum redeployment range of 1,000km (from centrepoint to centrepoint of provinces) (figure taken at random), or having an ETA after a deployment order was given based on distance (with the unit returning being reset in the void if the province was lost before arrival)
Issue: Strategic redeployment, army level
The ability to strategically redeploy as an army rather than as individual divisions is sorely missed. To redeploy a 12 unit army I need at least 24 clicks to put them in the force pool, 24 clicks to put them back on the map, and dragging a selection box and merging to reform the 12 unit army again. (Or having deployed the first unit, I can try finding it again in a list of ALL the armies the other units could possibly be attached to - this can be a
very long list given the continent-spanning warfare of HOI, and deploy the remaining 11 units one by one).
It would be very nice to have a button to redeploy all (like the reinforce all button) that redeployed the entire army. It would then be put in the deployment pool with the same icon as the one shown on the map and with the army name and could then only be deployed as an army from the pool. Hovering the cursor over the army in the pool would give a breakdown of units.
Yes, this is a major change to the core functionality of the redeployment pool, but it is a sorely missed one given the number of divisions the player is expected to handle simultaneously when playing a major.
Issue: Rebasing of aircraft
The creation of sufficient landing strips and storage facilities should perhaps not be instantaneous. A possible solution would be to reset organisation to 0 following rebasing, and not allow planes to take off unless they had, say, 15% organisation. (And perhaps give planes a downtime of a number of hours at 0% immediately following a rebasing?)
Issue: "Finish" the event command system
HOI is supposed to be a finished product. We paid for it, and all that usual stuff

And given that, it looks rather unprofessional when several actions in the scripted events do nothing at all but have a remark "#TODO_add the commands and system#". Yes, I'm perfectly aware of how publishing deadlines can wreak havoc on development and how the important thing is to get something that works on the shelves, but it
does look rather rushed and sloppy. Whether the intention is to add the functionality in a later patch or whether the current state is deemed good enough, a finished product shouldn't include "TODO"s where the customer can read them - much better to leave them out and tell the customer that it is an enhancement if it is finally added
(TODO's internally in the code where nobody notices is a different issue

)
Issue: cf. Manual, Neutral vs. Neutral: If the aggressor is a minor power, there will be no global political repercussions.
Boy, is this true. Unfortunately. And there won't be any local repercussions either. Nobody gives a flying fuck that Nationalist China conquers every Neutral nation westwards up to and including Austria and Czechoslovakia. And Japan, the Phillipines, Mexico, and central America. Majors neither protect their puppet states nor their political nor geo-strategic interests.
Given that HOI is a game of "Global Conquest" where players are allowed to "Completely manage the country of their choice" in which you can "launch devastating offensives, form alliances, research new technology, hire and fire diplomats" and that "the options are nearly limitless" (it is written in the manual so it must be true

) this is a major letdown, though it is almost certainly be design.
Please make them care.