My number-one choice would be the game you see in the video section.
Second would be maybe Section 8. Fable (series). Halo 4. Halo Wars.What bout the flood?
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Eternal Darkness: Sanity's Requiem and Metal Arms: Glitch in the System are both games I consider to be underrated. Also, as far as FPS games go, the TimeSplitters games are quite underrated.