Here's the boat I'm in: excited about playing Fallout 3 (mainly because I loved Oblivion) but woefully ignorant of the entire past series, which I understand some people are rather fond of. If that describes you too, you should really watch this excellent Fallout retrospective that Gametrailers put together.
It does a great job of not only showing you all the Fallout games themselves, but also contextualizing the history surrounding their creation. From what I've played of Fallout 3, anyone can jump in without prior experience and get up to speed fairly quickly, but I feel a lot better equipped to appreciate more of the game's subtleties now that I've seen this.
The video also made me realize that there's no way I can go back and get into those two original games now. They're just too far removed from modern game design and especially modern presentation; I'm too spoiled by lavish 3D visuals and streamlined control schemes to be able to look past the exceptionally dated nature of these games, classics or not. On an academic level, I can certainly appreciate why so many people love them, but recapturing that magic a decade later just isn't in the cards for me.
Then again, I'm not worried about it; the new game is out in a matter of hours now.