I'll probably take some heat for this, but I like the First/Third person playstyle. Not that I hate isometric games or anything, but I do tend to feel more immersed with the new engines, more so with New Vegas but still. (At least until a glitch sends a Deathclaw crashing down like a meteor or when a raider sinks into the ground.)
I'm not a fan of the "Disjointed setpieces scattered across the map" thing Bethesda does. It's sort of okay in TES, but not in Fallout. That said, some of those setpieces are very enjoyable in their own right. Whether it be the cartoonishly evil Megaton explosion or something like dealing with Harold or The Pitt where you end up facing a dilemma (If you're roleplaying with your morality in mind.) that could leave a good character without a satisfying "Everything's fixed" answer. Andale was pretty interesting, but I think it's more memorable because James lead me there on the way to Rivet city so we had this child/parent showdown with them when their secret was revealed. On its own, it's pretty much a one-note story but I kind of added my own story to it with the idea that James and my Wanderer had to rest there for the night or something. I guess I can't give the game credit for that, except for the atmosphere.
The atmosphere of Fallout 3 makes little sense* but it's hard to deny the atmosphere of not just the overworld, but even in certain quests and areas. The Dunwich Building is an atmospheric location, for example. Though I think New Vegas tackles atmosphere better, but it's more subtle so not everyone catches on. Pick your poison kind of thing, I guess.
*I try to just accept the state of the world as the Sooper Mutants being there never allowed for civilization to grow into something like the NCR. Even that's a stretch, though.
I suppose I like exploring. I felt dirty for playing a Fallout and spending so much time not speaking with people about their problems but I spent a lot of time just wandering the sub-divisions of Washington D.C. It was fun. I don't think the exploration in and of itself kills the Fallout vibe so much as there just being no real sense of an overarching world. I would say the exploration focus is just a different take on the game, but the towns being so disjointed like they're in completely different worlds is unforgivable.