Oblivion with guns with a fallout atmosphere would even be ok. Oblivion is a lot of fun.
I'd prefer a few tweaks, though:
I played Oblivion on the PC, and am now playing it on the x-box (so I don't have homebrew mods like I do on the PC version), I am finding I do not mind the hated "leveling" as muich as I thought I would. In fact, I still feel the sense of growing in power, but I'm still challenged everywhere - they did this pretty well, to be honest. My one complaint here is I would rather see less bandits with Glass Weapons (etc), though - that stuff should be rare. I would also like the chance, even a slight one, of finding BIG loot at low levels.
Spread the world out some. While Oblivion is big, I do not get a sense of the size, because there's a dungeon/fort/ruin/cave every thirty feet.
If there will be join-able NPC's, it would be nice if they didn't jump in front of your attacks... Oblivion doesn't rerally have joinable NPC's, but there are some missions where you accompany someone - your ally is ALWAYS in your way. It's annoying.
As already mentioned, slower degrading weapons would be nice. I do not mind having weapons break, having to scavange, etc. That's preferred, actually. Just not quite so fast as Oblivion (although now that I am journeyman in Armor, it matters little)
I LOVE Obvlion's "you get better if you actually do it" way of leveling as opposed to the experience point way. I hope they keep this.