Comment by etempleton

Most games were not backwards compatible between Xbox and Xbox 360. They had to do work to make game work and prioritized the most popular games, most notably Halo. With that said, there were certain features that did not work properly. There was a Halo 2 map they took out of the online pool because it used a heavy fog effect that would not render on 360.

From 360 to Xbox One there was a similar situation where they would patch individual games to work, but because it was at least partially emulated, publishers had to sign off on allowing their game to be backwards compatible.