Mount and Blade and Mount and Blade Warband. Not flashy games but they offers deep customization, medieval backdrop, multiple factions. There's really no story to speak of, you kinda make your own.
http://www.newegg.com/Product/Product.aspx?Item=N82E16883227371 Not a bad machine, the video card has been getting good performance in Crysis 2. Windows included too.
I love the trade the Braves made in getting Bourn, gave up next to nothing to acquire him. Still, would have been nice to add a right handed bat and relief pitcher.
NeverWinter Nights. I saw the sun rise on numerous occasions while playing that game.
Dragon Age Origins
Mass Effect
The Void
Torchlight
Doom 3
Brothers in Arms Road to Hill 30
Hitman series
Baldur's Gate
Far Cry. Damn those Trigen
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