Fallout 1 is a well focused game. It's perfect. Everything is well designed, well thought-through, makes sense, and fits the theme and the setting. The Master, the "villain" of the game, isn't really a villain (he thought that he was doing the right thing), which is why it's possible to defeat him without a fight.
Fallout 2 is a "mix of everything" game. It's a game designed by a bunch of 13-year olds following the unbeatable "won't it be cool if the game had...." principle. It has huge gangsters with tommy guns running casinos, it has yakuza with samurai swords, it has so many weapons that you can switch to a new gun every 5 min, it has more lulz than the Codex, it has a king-fu fighting town, it has scientologists with celebrities, it has tribals, aliens, drug dealers, talking deathclaws, and even real GHOSTS. The game's a joke.
The main villain is a stereotypical "I kill everyone for the lulz" villain who looks like a giant robot. (the 13 year olds strike again!) You can't reason with him. The only way to beat the game is to fight him.
Overall, I feel that FO2 locations, NPCs, and quests are clearly inferior to FO1. While FO2 is better than most games (mostly due to being a sequel to a great game), it failed to deliver the quality of the original.