Ai acts less weird on the battlefield.It tries to flank you with it's light cavalry or infantry.
It searches for easy targets for cavalry charge meaning it wouldn't charge into ready spearmen
It retreats.I don't know if this is present in RTW, but I just hate it when I load up a battle, and the AI just retreats.....
AI does retrain Its units, meaning you will actually see some nice veteran armies ready to be killed
I don't know that movement is improved, but the cohesion of units is improved.The units have less chance to just spill on the battlefield.This happens with phalanx a lot in RTW, or when you move your units a lot on a tricky terrain(walls, cliffs, etc.)
AI invasions are present in BI more than in ALX, but they are still present.
ALX cannot use special abilities from BI like shieldwall, schiltrom, hording, swimming....