Aha.
Call of Duty 4 sold on its own merits. The previous game, CoD3, was quite good, but by no means excellent. The launch week was good, but less than spectacular. The legs were brilliant, and with good reason. CoD4 is an excellent game.
Call of Duty: World at War. Sigh.
They took a massively successful FPS, CoD4, put it 60 years in the past, added a flamethrower, and made a bunch of tweaks. I think we can all agree that without CoD4, World at War would have been a mess. They took IW's incredible game, and improved it. But without IW's incredible game there to work from, there would have been another CoD3.
Call of Duty: Modern Warfare 2:
Well, we have CoD4 and CoD:WaW. Both excellent games, one copying the other a fair bit. IW will have had less than two years to develop this game, so we probably won't see a large overhaul. However, there will be more differences between CoD4 and MW2 than between CoD4 and WaW. I say this will outsell both games.
(Former) Lead Moderator and (Eternal) VGC Detective 
