Yeah, part of me wished I'd had waited for the GOTY edition.
But, certainly...without a doubt...Fallout 3 offers the best DLC for any game. It's just the game that keeps on giving.
I've spent a little over...I dunno, maybe 60 hours or so. And I have not beaten the game yet. I've got two files, one good and one neutral...and even with those two I'll often find myself just wandering the wastelands just for the hell of it, or maybe just to barter.
If you love Oblivion...and Fable 2, I think you'll love this. It's sorta of the same idea, only in a completely different setting.
I'll have to hand my twenty bucks for the last two DLC, but maybe once I'm through the Pitt.