In my opinion the AI is no where near as good in 2 as the past games. Generally playing with 2-3 other intellegent civs, and not really having any problems winning. Lets see :
1) The AI doesn't use any speed. So when they get to you they're a generation or 2 of tech back. They're transports are sitting ducks as well because of this.
2) The AI doesn't guard anything.
3) The AI doesn't seem to value good ships, just masses of crappy ones.
4) The AI doesn't put enough focus on capturing, or destroying your resource starbases.
5) The AI doesn't put enough focus into upping it's pop centers.
Don't get me wrong I love this game. But IMO, the AI isn't up to par with the older games. Perhaps this is just because the great diversity in strategies caused by the new tech tree, and ship designer. IE the AI can't quite be so well scripted as in the older games.