Mario (NES) + Portal
This game is amazing and for some reason I can't pull myself from it. I t has all the original levels of Super Mario from the NES, with the added bonus of having a portal gun, then there is a level set with portal-esque levels, your own map editor, customizations, up to four player co-op, and other random add-ons.
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Intel i7 3.40 Ghz, 8 GB RAM, 1.5 TB HDD, AMD/ATI Radeon HD 6770, Quad Boot : Windows 7, Ubuntu 12.04, Gentoo, and Arch Linux