Absolutely brilliant is the main thing i will say about Fallout 2- everything from the underused (in other games) black humour to the rich and detailled back story and characters.
However i feel that a warning must be given to those who either a) played Fallout 3 and wanted to try out an earlier one or b) belong to the current that was brought up on real time 3D RPGs.
Fallout 1 and 2 are very different from these and with its old fasioned interface it can be difficult to be get in to or understand. I myself am in a and b and initially had difficulty getting to grips with the game (especially in picking useless traits etc on my first try). However perserve and the true gem is bale to be played.
Recommend fully but check out before you buy that its your type of game.