One of the most requested features for what is now considered the current generation of consoles was backwards compatibility, an understandable demand considering how relatively sparse the games library for both the PS4 and Xbox One were at launch. Unfortunately, backwards compatibility was swept under the rug by both consoles until November 12th, when the Xbox One will receive an update that will effectively allow it to emulate the Xbox 360 and play games that were once exclusive to it. While only 104 games will be available as of November 12th, more will be added as time goes on based on community feedback (which can be submitted here).
Some of the most notable games that will be available for Xbox One backwards compatibility include the entire Gears of War series, almost every game that was (and will be) available for Games with Gold, and Castle Crashers. Oddly enough, while the first Mass Effect game will be available for backwards compatibility, none of the sequel games will be available. Similarly, Halo 3, Halo 4, Halo Reach, and Halo 3: ODST are missing even though Halo: Spartan Assault will be playable.
The list of Xbox One backwards compatible games can also be found here, on Major Nelson’s site.