0ad is great. I play it quite often with colleagues after work. That said, the pace of development is very slow, path-finding is pretty broke for the majority of formations and it can get very slow when dealing with the formation animations. Some of the core maps are fundamentally broken also (siege weapons and elephants can't fit through the mountains on one map making it almost impossible to win).
As in they aren't randomly generated? Or any placement of mountains creates an impassable pass?
By the way, a new Alpha came out last week. Might be worth a test drive as they're constantly improving the game.