While the BTS AI has definitely had more time to develop, I feel the Civ IV AI was better than random. My impression of the Civ V combat AI so far is that it's actually worse at combat than the barbarians. Combined with a combat system with a much higher potential for blowouts and you can literally beat 4 warriors, 3 archers, 2 swordsmen, 2 scouts and multiple cities using only 2 horsemen and a scout. (That's the example from my last game.) This is not by abusing known quirks of the AI, or even being particularly clever at all. It's just straight up attacking the closest guys on every turn you don't need to heal, and you literally never lose a single unit. Seriously! It's not like I'm trying to not lose any units. On one turn, after killing a warrior, I left a wounded horseman in a far forward position in range of two archers and a sword. The archers attacked my fortified scout on the hill behind him instead, accomplishing nothing, and the swordsman walked out aimlessly onto the flatland next to the horseman. It's just unbelievable.