If you want a game with nearly infinite replayability, I nominate Fallout 3. As I get further into the game, I'm beginning to respect Bethesda a bit more for their effort. Still far from perfect, but at least an 8/10 from me, which is the equivalent of a 9.5/10 from most posters on this board.
Mass Effect is another solid choice (and a slightly better game than Fallout 3 IMO), but it's FAR shorter with less replayability.
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