I just finished playing Fallout 3 after a four-hour late night session beginning at Lamplight Caverns and ending at the Jefferson Memorial, and my verdict: Fallout FTW. That game controlled my spare time for the last month, as I roamed the entirety of the Capital Wasteland, killed anyone who got on my nerves and plundered the wealth of the wastes. I racked up achievements, roamed across the D.C. mall and just generally enjoyed the hell out of it.
I was especially impressed because I went into it very skeptical - a huge fan of the original two games I was worried the new gang cracked its head on a beam and forgot that it wasn't Half-Life 2 or Gears of War, but that wasn't the case. It mixed (for me) the perfect combination of cheerful pre-war mentality and Mad Max-esque gritty realism, the barter-based economy that uses murder to replenish funds, reappearance of Harold and Dogmeat and a surprisingly entertaining V.A.T.S. system. Add in the ability to compile MacGuyver-style weapons, an interesting main narrative and rendition of post-apocalyptic Washington and you've got a very immersive and enjoyable game.
Some qualms were there (after level 20 it just turns into a shooter, you get far too much loot if you raid everyone you fight, the game is just too big to experience on one play but too big to work up enthusiasm for doing a second run right away) but all of them were squashed by the sheer enjoyment of strolling the wastes and being able to blow the head off a raider from 200 feet away.
So, in a nutshell, I'll back any and all Fallout games, and if the original developers have their hands back in it I can't see that as a bad thing.