Really fun, challenging game with a (mostly) friendly player base.
The single player I found to be a real time sink as I see it as a challenge against yourself. The bots ARE beatable but very hard (especially the final two which are cheating A.I (It's stated in their descriptions)).
I found myself constantly trying a new design scheme for a maze seeing what worked best.
However the downside to the game (more in multiplayer than Single Player), there's too much emphesis on the earliest moves in the game. If you make just one small mistake against your opponent, it's can be really hard to come back even if they make mistakes further down the line. You're punished more the earlier in the game you make the mistake.
Great game well worth the money especially when on sale (which has been happening a lot, I ended up buying it between sales :( )