Fallout 3, while a decent game on its own, felt more like a collection of cool shit, rather than a living breathing world which coincidentally is what the original Fallouts were about and why I liked them so much. To quote Tim Cain on this "My idea is to explore more of the world and more of the ethics of a post-nuclear world, not to make a better plasma gun". Fallout 3 failed completely on the world and ethics and succeeded on the plasma gun bit, which is missing the point. Storyline did not make sense (water purifier, that frickin ending), plot holes of epic proportions everywhere (characters dying than coming back to life, comes to mind) and my god the world design...I mean what do people at Washington eat 200 years after Apocalypse, when there's no fauna and when there's no fauna there are no herbivores to herd yet you see brahmin everywhere apparently eating mud, or perhaps they're photosinthesising, with that in mind, what do people actually breathe? On a more subjective note. I hated every single character in that game. They all came off as condensending, ungrateful shallow and annoying bastards. And so on.
New Vegas fixed pretty much all of that, while also rebalancing Skills and Perks, so now you can not max out everything, but you can, you know, roleplay, have a specific character, with specific abilities rather than a be all end all Gary/Mary Sue. It also didn't rely on combat that much, which is a plus. On another subjective note. Vault 11 was one of the greatest gaming moments I had since The Hotel in Bloodlines.