User blog comment:Callofduty4/Why is it a sin for Treyarch to rip some aspects off of Infinity Ward but OK for Infinity Ward to rip off some stuff from Treyarch?/@comment-1405970-20091224012317

As Peter Griffin says, the revive system is basically the same for all co-op/third person games. Waves are basically the same, I mean, Halo ODST's Firefight, GOW's Horde, all are similiar. The Ranger model yes.