LoL is a lot of fun in co-op vs AI with people you know (if they're the sort you like playing games with, at least), though it doesn't take long to get good enough that the AI (despite periodic improvements to it) really doesn't have a chance at beating you (on the plus side, that means you don't feel as much of an urge to spend money to get specific champions or faster access to runes: no competitive need). If DotA2 has co-op vs AI I'll probably play it at least for a little while.