I never had to opportunity to play this classic until GOG offered it, and I want to say thanks for making it possible on Win XP.
Pros: The main thing Fallout has going for it is the atmosphere and conversations with NPCs. Both make you feel really drawn into the game. I also love all of the "nudge nudge" humor and pop culture references in random places. The graphics are good and the animations are some of the best I've seen in an isometric game. Combat is also pretty exciting, although once you find the best items (Power Armor, Plasma Rifle), it gets a bit easy because almost no one can stop you save for an unlucky critical hit.
Cons: My issue with the game is its clunky interface, especially with inventory management and buying/selling at shops, which can grate on your nerves after awhile. Also, Fallout has a steep learning curve initially - newbies who build what they think is a "cool" character may find it more difficult to complete the game than if they had built the "ideal" character.