That's wierd. This is a forum for a Post-Nuclear Roleplaying game.
Restrictions make for great RPGs for a few reasons: one has to put effort in developing a unique character and skillset, and has to make choices during the game as to what one chooses to see and do. It also adds replayability, because you "can't see everything in one go" as another poster writes.
One of the dumb things about Fallout 3 is that every character ends up playing exactly the same, maxxing out every skill and doing everything for everyone. By comparison, even the classic Fallout diplosniper plays differently depending on your approach to the various choices the game presents you with.
/sidesteps back on topic
Fallout 2 is a big, open game and there are a lot of quests to be unlocked. The quest structure is indeed closer to Fallout 3 than Fallout 1: 'player walks into town with unique problems that have nothing to do with main quest, solves them because solving unique problems is cool, and because let's be honest I need XP.'
The difference is that the quests in Fallout 2 intertwine into a larger back story, and impact the game's ending. Different character "builds" (lol your terms confuse me lolol) approach each quest differently, and your actions matter across the game world. For example, I threatened to blackmail the preacher in Vault City, later delivered his briefcase to Bishop in New Reno. There was a note in the briefcase that exposed me as untrustworthy, and I had to fight my way out of Bishop's casino, killing dozens of innocent patrons in the epic crossfire...now that's good quest design.