I'll preface my comments by saying that I'm about as undemanding a CoE buyer as there is since I purchased it as a thank you to IW for Dom 3 and wasn't really concerned about whether I'd like it or not. I'm glad people are enjoying the game and I hope it sells well.
Having spent some time with it I'm of the same mind as elmokki as regards luck vs. decision making. Currently luck plays too great a role in the game for my taste. But looking at the pace at which things like modding are being added to the game I'm pretty optimistic that CoE3 can add more in the way of decision making - without sacrificing streamlined gameplay.
I should also mention that I've only played the game SP, don't really plan on playing MP, and view the game as having a SP focus. Given that, my focus is on fun rather than game balance.
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Allow more control over spellcasting. Probably my favorite class is the warlock. It's exciting to get a spell that attacks an entire row ... but pretty frustrating when the AI decides to start off combat with a spell that attacks just a single or handful of opponents instead (obviously front loading damage is good since it reduces the number of hits my troops will take). So what about giving the player complete control over available spells, even to the extent of just selecting one to be cast repeatedly (and if it could no longer be cast then the game would default to the complete spell list)? Edi mentioned here or on the CoE forum that there are some very powerful spells and if you could specify that they be cast repeatedly it would be OP. But I guess I don't mind because from a SP perspective if I get a great spell it's damn fun to watch it annihilate my opponents.

From a MP perspective this could be a problem but if the game developed more tactical depth this could actually present some interesting possibilities - I know my opponent has a great spell and I'm counting on him using it so I attack with a force designed with that in mind. Like I said, I don't think the game currently has that depth, but the potential is there.
If that's a nonstarter then what about a limited scripting system for 1-3 turns? Something along the lines of:
Round 1: cast fire attack at entire first row of opponents
Round 2: cast armor buff on entire first row of army
Round 3: cast strength buff on multiple units in first row of army
Now, you'd probably want to leave the back row out of this so people can't just target mages. And this would be optional - you could choose to ignore scripting and just let the AI handle as it now does so it wouldn't add complexity for those that don't want it (but I bet most people would use it

). And even if you did use it, it wouldn't add the kind of additional burden scripting does in Dom3 because CoE has far fewer commanders to manage.
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Allow more control over unit placement. Thinking over how to provide some control over unit placement, making it army based seemed like it would defeat the purpose of having a fast playing, low micro game. But making it unit based seemed like it might provide some degree of control over your armies without adding much to the micro. Just as is currently the case, each unit would have a default rank and you could use that rank and never use any of this functionality. But if you wanted, you could pull up a list of your current units and change their rank. Perhaps something along the lines of FrontA, FrontB, Middle, and Back. FrontA would be the first units chosen for the front line, after that would come FrontB. So some battles I might want my swordsmen up front to take the first hit and then my summons to clean things up after my mages had softened up the opposition, other battles I might want my summons to go right to work on the enemy.
Again, just like the suggestion with scripting this would be optional and could be ignored if the player didn't want to deal with it.
Now I suspect neither of those ideas are trivial things to do and would involve considerable new coding and maybe there's an easier way to implement decision making for the player but I think these are the kinds of things that would add depth to the game.
I also have a couple of requests that I think would make the game more fun.
* Please (really, please)
add a slider to control indie spawn rate. I understand the era chosen effects this but I'm thinking of a global control. Personally, I find indies maddening - I want to focus on fighting my rivals, not tracking down deer and bandits. Also, in the weeks leading up to the release of CoE3 I played a good amount of CoE2 and, unless I'm misremembering, indies didn't seem to be such an aggravation there. Was the spawn rate turned up for CoE3?
* I think it would be very helpful for
AIs to start the game with an immobile commander in their capitol, something like the barbarian's totem pole. This would prevent them from losing the game by sending all their commanders out in the field and having them killed or having a small force of indies walk in and take their capitol, resulting in them losing the game if that's their only city. I can't really think of any drawback to doing this. It would mean a bit of a tougher fight for the player to take the opponent's cap but I don't see that as a problem.
* Lastly, in CoE2 the warlock had the ability to bind with an element, which would make him tougher. He still wasn't anything like the stronger monsters but it improved his battlefield survivability ... and it was just cool. Any chance of getting that back?