I've noticed a shortcoming in the AI with respect to melee units.  Many times I'll have a severely injured unit, and the AI could just take one step over and attack / finish it off.  However, if the AI controlled melee unit has another unit next to it, the AI will never consider moving .  Thus, the AI is not not considering the best target to attack, or best place to land a cleave, etc.

With archer units on the other hand, the AI will consistently step back so that it can fire at my weakest unit.  The AI should be doing the same for melee units that can reach another target.