XCOM: Enemy Unknown art director Greg Foertsch conducted a GDC 2013 panel called Art Direction Autopsy: XCOM: Enemy Unknown. Foertsch shared a few internal videos chronicling the different directions considered by Firaxis Games, and was kind enough to share those videos with Joystiq.
Above, you can see a video with a more survival-horror slant – a prototype with methodical pacing, centered around a lone farm house wrapped in dark atmosphere. Jump past the break for two more prototype videos.
The second video lacks a lot of the cover that is so crucial to success in the final version of XCOM: Enemy Unknown, and carries forward the lone farm house and isolated countryside themes of the first prototype. It also shows early UI elements and a sweeping radar-like line-of-sight mechanic.
The final pitch video highlighted ideas for a more cinematic XCOM: Enemy Unknown experience, as two panicked soldiers find themselves pinned down by a pair of Mutons. This shows the genesis of the cinematic kill cams that feature prominently in the final game.