Ive never played a single expansion for Fallout 3, sadly. That was part of the reason for getting the GOTY on steam, too bad it didnt work on my lappy.
Broken Steel is essential IMO, it was kind of a scumbag move to make it paid DLC
Operation: Anchorage adds the most OP armor in the game regardless of your specialty (partially due to a bug), but I don't mind
I've played and beaten Zeta before, it's not too special unless you've got an Energy Weapons character (the supply of Epoxy is nice though)
I had just started The Pitt when my friend took back the game he'd lent me for Xbox so I don't know much about it other than what I've picked up from related wiki pages
I think I started Point Lookout but I don't remember much of it, IIRC it was filled with those loving Ghoul Reavers
I know that feel though, I've got Skyrim on my Steam account and I can't even play the damn thing because my PC is too old