Before I get this post rolling, I should probably point out I've only played Fallout 3 from the whole Fallout series. Add or remove the validity of this post as you feel fit.
I think a lot of people didn't like New Vegas because it seemed a lot like Fallout 3, but was sold as a whole new game. I know it was different, but I can see the similarities that would make people feel it wasn't different enough.
As for the Fallout 3 hate, I haven't heard much of it. I'm guessing some people hate it purely because it's not Fallout 1 or 2, but that's a silly reason.
I think a lot of people didn't like New Vegas because it seemed a lot like Fallout 3, but was sold as a whole new game. I know it was different, but I can see the similarities that would make people feel it wasn't different enough.
As for the Fallout 3 hate, I haven't heard much of it. I'm guessing some people hate it purely because it's not Fallout 1 or 2, but that's a silly reason.