The AI in GC2 tends to be somewhat passive. They will build ships and harass you, but they tend not to launch an aggressive campaign to actually take your worlds. In the many hours i spent playing on higher difficulty, i can count the number of planets the AI swiped from me on one hand.
If you enjoy a long, slow, empire-simulator kind of game, GC2 is just fine. If you want something more aggressive and tense, GC3 already provides a more interesting experience as-is. Again, it isn't more difficult (yet), but it is more interesting.