I've only played 7 hours of Fallout 2 (which is mostly comprised of trying to get to San Fransisco, getting to Navarro, realizing that small guns suck balls after around 3 hours of playing, making a second character using energy weapons, and getting raped by Enclave patrols), but so far I'm having a great time with it. Fallout 3 introduced me to the Fallout series and I'm glad about it.
edit:
Arlocke said:
There are two main reasons:
1. Because it's not very good. Bad combat system which involves a lot of running backwards from monsters who just rush you every time. Crap writing. Slightly dated graphics and completely horrendous animation (which was much improved in New Vegas however).
2. Because it totally ignores the established canon of the Fallout universe in a way that's almost insulting.
Well there's a couple of issues with that.
1. And the original Fallout combat system was so infinitely better. The old system is too awkward and arbitrary. Too many clicks and god help you if your enemy starts running away. It works, but it really could have been streamlined. I'll agree that writing wasn't all too great, but I never found it bad enough to actually dislike the game because of it. As for graphics and animation, you do realize how big Fallout 3 and New Vegas are right? It would be a complete ***** on the processor if it they had tried to make it better.
2.Fallout: New vegas rolls with canon pretty well I find and Fallout 3 doesn't make too bad of a mockery. There are only two factions mentioned in Fallout 3 that were also back in the west: the Enclave and the Brotherhood of Steel. What they do to the Enclave is pretty bad (that was not fucking advanced power armor mark II and how is the Enclave still around?!), but the inconsistencies with the Brotherhood are negligible I found. They openly say that they're different from the western Brotherhood anyway.