IMO, it's the Wasteland setting that made Fallout 3 so popular, given that game itself is both much weaker than previous TES games and especially Fallout 1/2. But if you're someone who likes open-world RPGs, it was a decent game.
I fairly liked it, though it's but a shadow of original Fallouts, and it can barely be called Fallout game at all - but, tbh, I can't blame Bethesda much, I really think they've tried their best, they're just not capable of doing much better, even Morrowind, arguably best game they ever made, is severely lacking when it comes to story and characters, and that's what original Fallouts were all about.
I can't say I expect much from Fallout 4, given they're doing it by themselves and not with Obsidian, but I will play it nevertheless - good WRPGs are rare these days (thankfully, revival of cRPGs is filling that void), so anything half-decent is on my list.