Fallout: New Vegas is a rather notorious case, in that a one point shortfall in Metacritic rating (84) made the venture unprofitable for Obsidian.
Fallout 3 has a 93 MC rating. Fallout 3 was admittedly really neat when I first played it, having never played the series before, but its story was really as linear as any Japanese RPG, and the ending was very anticlimactic, to the point where they released a DLC to fix player complaints. It has a lot of nice set-pieces for its time.
New Vegas outshines it in every way. They did the best they could with the game engine to improve the visuals. It doesn't look hugely different, but it is brighter and more lively, and manages to convey that the Mojave Wasteland is a land trying to heal from the Great War. The actual game mechanics and story structure are where NV truly shines above its Bethesda-made predecessor. There are true branching paths and multiple endings, the stats really mean something outside of combat, and the writing is much better. Rather than a general "karma" rating, you had a reputation with each faction - and both your good and bad interactions were figured into that reputation; by helping the NCR in some missions while working against them in others, you could obtain a sort of "mixed" reputation with them, for instance, instead of being outright villified or lionized depending on what your most recent action with them was. Your choices had weight in part because many of them were irrevocable, unlike 3 (and 4). And these things all factored into the endings.
Was NV perfect? Absolutely not. It had all the same flaws and bugs that 3, Oblivion, and pretty much every other Bethesda title had. Given that, other than already having a basic framework built on the previous games for them, they had less resources and money to make the game than Todd Howard did, Obsidian did a fine job.
In retrospect, I would reverse the scores of the two games, or at least drop 3 down to a 87-89 range while awarding a 93 to NV.
