Both great games. The online multiplayer of COD4 was crappy at first.. Too slow.. but the recent updates have made it awesome...Halo is the basis that all of these online multiplayer are made with. I think because of the lack of reality of H3. (not that juggernaught and Martydom are reaistic) hurts the game a little. I like the campagin of H3 better but overall COD4 is a more fun game to play..