Fallout 2 really just does everything you'd expect a good sequel to do, keeps the same core gameplay while adding on top of it and correcting things that didn't work out in the first one.

Compared to Fallout 1 there's a lot more emphasis on different factions and their beliefs that really brings a lot more depth to the game, and eventually culminates with New Vegas, which is probably the real sequel to Fallout 2.