The entire S.T.A.L.K.E.R. series.
S.T.A.L.K.E.R. Shadow of Chernobyl
S.T.A.L.K.E.R. Clear Sky
S.T.A.L.K.E.R. Call of Pripyat
(No I didn't type each one. Ctrl-C, Ctrl-V. Try to type S.T.A.L.K.E.R. fast and see how annoying it is.)
Metro 2033 as stated. It's a spiritual relative of the S.T.A.L.K.E.R. franchise, and if you have such a PC beast as you suggest, then you're in for some friggin' eye candy.
The Total War series:
Medieval 2: Total War
Empire: Total War
Napolean: Total War
Company of Heroes, you could do without the last expansion, Tales of Valor, it's shit.
Anno 1404: Dawn of Discovery
The Penumbra Series:
Penumbra: Overture
Penumbra: Black Plague
Penumbra: Requiem (2nd part of Black Plague)
Vampire: The Masquerade-Bloodlines (You said 5 years eh? Close enough.)
Any MMO that you take interest in, or two I'd recommend:
EVE Online
Fallen Earth
Any game you take interest in, is better on PC.