I, for one, am against any sort of tactical interactivity in battles. Why? There are two reasons:
1) Tactical battles break the strategic focus for the player. When you play 4+ battles in a Total War game, with each lasting 10 - 20 minutes, you really lose focus on what is going on the strategic level. The length of a single campaign is drastically increased, and let's admit it, the tactical battles soon get repetitive, because the AI is predictable.
2) Either the tactical battle mechanics is trivial, or the AI sucks at it. I haven't seen any other option - in Total War games, the AI sucks, allowing the player to achieve unrealistic victories against stronger opponents with unrealistic low losses. That distorts the strategic level quite a bit - the AI must be able to predict battle outcomes (at least roughly) to formulate any sort of reasonable plan.
I really enjoyed the system in Dominions 3 - you do the preparation, and the battle plays itself non-interactively, you can only watch. That said, it would be interesting if the ruler could make decision that would affect the troop composition more. I believe that England had a law that ordered every young male to practice with a bow, and regular tournaments were held - and that gave English their famous longbowmen. The power juggling between the four classes in CK1 was quite a nice touch. The generals should be able to arrange troops in a meaningful manner, according to their martial stat, and tactics should matter more.
However, according to what I read about warfare in Middle Ages, the troops were notoriously difficult to control. The knights were impetuous, deciding to attack when they wanted (Creche), the mass levied infantry was untrained and of low morale. More elaborate tactics than initial formation and decision when to commit were hard to execute.