How about S.T.A.L.K.E.R it has a similar world environment like oblivion, and I am sure if you turned up the settings it takes a little power for it to run.
if your a fan of counter strike and zombies try left 4 dead when it comes out, also bf2142 is pretty fun, and if u get a a 8series card with dx10 u might wanna try lost planet since it uses dx10 and it looks awsome.