An absolute favourite PC RPG, one so great that I've come to know it almost as well as a childhood friend.
It's hard to quantify exactly but every nook and cranny of the game seems to be infused with a sense of nostalgia for post-war Americana - whether its comic books, muscle cars, science fiction movies, or 'Nuka-Cola' Fallout lovingly sends up the culture which has inspired it. There's a real sense of melancholy and nostalgia that pervades the game for a lost (cultural) world which is what lends Fallout its peculiar power. The wasteland in the game is as much a graveyard for the past as mediated through cultural products [the rotting buildings, decrepit billboards, and other such examples of cultural detritus] as it is a post-apocalyptic environment in its own right.
Even though there's no reason to I've played through this game probably more than a dozen times, and I virtually never replay games. The game world is just so peerless in its design.
That said the gameplay does have a few flaws. The system for moving/interacting with objects is not immediately the most fluid. Eventually I found after a while it became second nature to switch between the modes and use the hotkeys, etc. The interface isn't as bad as the one in Arx Fatalis at least. For some the combat is too slow, rendering it a chore to wait through all the enemies turns. I've had more than a few friends comment about it to me, neglecting the fact that an options setting could've alleviated their problem in a few seconds. Fallout Tactic's transition to real-time was a failure in my opinion and doesn't improve the gameplay in any significant way.
For me the only significant flaw with Fallout is that there's simply not enough of it. A few more quests would've been nice, more of a story, a longer game - but on the whole I can't really complain. It's short and cogent, delivering a unique, impressively detailed world. It's about as far as you can get from the Elder Scrolls games which offer massive but fairly uninteresting worlds with no eye for detail whatever. That the Fallout series is now in Bethesda's hands is one of gamings many cruel ironies.