To help tactical combat be more meaningful with more choices (even the AI can use) in an easy way, I suggest adding a small feature you can find in the superb free tactical game The Battle for Wesnoth, which they took from the revised AD&D rules. Wesnoth implemented it brilliantly and easily: They call it Zone of Control. This means:
- any unit or group which moves into a square adjacent to an enemy unit or group which is able to make an active valid melee attack can not move further until the next round of initiative. It can attack the enemy it moved adjacent to, but it cannot move past it without ending its initiative turn (by performing a valid attack or by otherwise using an ability).
This mechanic would be functionally equivalent to having a layer of strategic choice on the tactical level. It would make strategy on the tactical battlefield much more important by transporting some modicum of decision-making in tactics to the phase of army-building: it would then thus become slightly less feasible to simply count combined attack values, for instance, to gauge victory, and would thus reduce the chances of being able to obtain tactical success by always following the same plan (hence reducing the chance for no-brainers with recourse to "bigger is always better"), and open up slightly more options: is it better to consolidate my resources here, by investing in a higher-level champion and bringing him to battle with a small escort, or is it better to diversify my resources there, by using a lower-level champion supplemented with a screen of melee fodder to protect a mage or some archers in the back? (This might also be interesting for some quests, where you might need to keep a particular fragile unit alive and transport it to tile T -- a single, heavy escort might not be your only, or best, option.)
The Zone of Control rule of TBfW is particularly good because it follows the "Keep It Simple" rulebook and is thus easy to understand and relativley easy to implement.