What do you mean by "generation"? Console generation? Considering a-RPGs are one of pillars of PC gaming together with MMOs (so, to an extent, RPGs), shooters (though not any longer, I guess) and all sorts of strategy games, that would be completely wrong. A generation of players, then? Say, 10 years period? You'd have Neverwinter Nights and Gothic 2 releasing not that long before Fable. You'd have KotOR releasing roughly at the same time, and Mass Effect, Witcher1 and KotOR2 3 years later. Fable is 5 leagues below all of these games.
I guess it's a small victory for Fable if it got you interested it the genre, but your opinion of it seemsto be coming simply from the feeling of novelty. People tend to overrate things that seem revolutionary to them. That doesn't mean Fable was revolutionary by any means, or that it was one of the best RPGs of a generation. It was a solid game, I won't deny that, but nothing more.
If there's one game Lionhead made that was really groundbreaking, it was Black & White. Or maybe it actually wasn't, and my opinion only comes from the fact that it was the first PC game (well, aside of Mario and Pong
) I've played?