The devs said the tactical AI is at its best on Hard. On Expert you're simply fighting enemy troops with an unfair morale boost.

Quote The ai is a joke whether it be on hard or expert. Just get 15 peasants and a katapractoi and stand on a hill.[/QUOTE]

Problematic? Yes. But I wouldn't call it a joke as it is among the best tactical AI in a wargame since Sid Meier's Gettysburg and the Breakaway games based on that same engine. My biggest complaint is the apparent lack of decisiveness the AI exhibits when attacking and its inability to stay put on good ground when defending. On the attack it's flanking maneuvers are impressive and appreciated but when it comes time to engage your troops it simply doesn't commit to a full on attack as it should. I'd say it suffers from a bad case of 'second thoughts'.