Summary
It doesn't get much better than this.
The Good
In brief:
Sub classes,
Wide variety of magic weapons,
Wide variety of NPC's that you are able to pick from,
Having allot more to do if you are of evil alignment,
Strongholds,
The fact that this game had a HUGE selection of spells,
Dragons ;).
The Bad
The only thing I can think of wrong with BG2 is that if I wanted to export and then import it got a bit tedious going through the starting dungeon time after time.
The Bottom Line
If you enjoyed BG1 then this game is well worth buying. The storyline is more complex and there are romances, which can get a bit annoying at times but they are still a nice touch to see that your characters actually interact, unlike BG1 where the only time the characters talk to each other is if you reform your party and let them go.