After about half the game I would’ve said that it’s a relatively uninspired successor to Far Cry with a pretty uninteresting story. However, the setting and story got a lot better in the second half, so it didn’t feel like Far Cry with the words “mercenaries” and “mutants” exchanged by “Koreans” and “aliens”. All throughout that, it was always technologically flawless and still leading edge. Not so long before the release in 2007 this level of detail would only have been found in rendered cutscenes.
I think I’ll eventually try Warhead as well and then the second part once it’s released, but I have to say I look forward to Modern Warfare 2 much more. It might not be as open as Crysis but every second of gameplay felt fine-tuned in COD4, while especially the tasks in the first part (infiltrate the next Korean basis) were not that intensive.