This mod only actually effects the historical battle, changing it so that there is merely one opponent of approximately equal strength to yourself and making it rely solely upon battle AI. I can't really say anything abouth the campaign.
I've fought the battle three times now (on hard difficulty), using different strategies each time. I won one by a mile, scraped a win in another, and got absolutely thrashed in the last.
The AI flanks properly, attempts to maintain battle lines/formations, counters aggressive moves pretty well, (meeting attempts to flank it with cavalry by either positioning spear units in the way or a unit or two of it's own cavalry,) covers long distances in a sensible formation, has performed a tactical withdrawal, attacked from multiple angles, hidden units in trees for an ambush, withdrawn archers sensibly when my infantry approaches (and vice versa.)
If the modder is being honest about not messing with the AI, the possibility of actually
losing an evenly matched battle has risen a hell of a lot. It's not perfect, but I'm damn impressed. Unfortunately, AI generals still seem to get treated as standard cavalry though.
EDIT: I'll post up my impressions on the actual game as soon as I get to play it. Hopefully this has been representative.