[onomastikon]

Trying not to repeat what the others said:

AI: better usage of spells (e.g. not casting Iron Warrios on *yourself* after casting Invulnerability; not casting Barkskin four times in a row; not casting precision-boosting spells on melee friends, etc. etc.)
AI: have AI-opponents build strategic fortresses and choose which provinces to attack when better
AI: choice of targets improved (reduced casualities from friendly fire)

Interface: Research Screen: Let us click on a school and be able to increase / decrease research spent with the arrow keys and/or by typing in a number
Interface: A hotkey which enables you to see which units a selected commander has under its command as well as their battle orders. Best would be a hotkey which simply links to the “set battle orders” section of the “troop command /t/” screen.
Interface: A hotkey enabling you to see which spells the selected commander can cast. Best would be a shortcut key linking directly to "set battle orders / cast a specific spell". (Or anything other than select province, hit "t", set battle orders, cast specific spell.) Give us some way of seeing which spells a commander can cast SIMULTANEOUSLY with which gems s/he currently has, preferably without having to enter the battle orders screen and actually change the battle orders (by pressing “cast specific spell”).
Interface: a hotkey enabling you to see which items a commander can forge – even if not in an area with a lab. Best would be getting this information PLUS spellcasting information directly from the commander’s screen upon having him/her selected.
Interface: let us see the personal gems (if any) a commander has when setting battle orders. Nice here too would be not only letting us see them, but clicking in that field lets us exchange them too (direct link to f7/exchange).
Interface: Allow commanders to “forbid” casting particular spells, or at least limit their use
Interface: Enlarge the Exchange Gems screen to accommodate more commanders. Let us be able to click on the commanders and change the gem number per arrow key (or better: typing in numbers) rather than clicking.
Interface: Alchemy screen: Let us be able to click on the gems to change and change the gem number per arrow key (or better: typing in numbers) rather than clicking.
Interface: the f1-f# screens pop up no matter what screen is currently active (thus allowing me to change items from my treasury, for example, while inspecting my army).
Interface: Giving an item to a commander automatically switches items should a slot be filled (e.g. I do not need to put his helm in the lab first before giving him a new one).
Interface: Either make default or allow a setting which lets you switch between default "returned actions upon invalid command", i.e. when you have a mage forging a helm selected and make some other (invalid) command, she goes back to "defend" instead of forge that helm and you have to reset.

for me, NO new modding tools / new themes / new races would be required in my opinion until some of the above can be addressed.