I have to assume that what bothers me is both the "realistic" context in which the cartoonish beheadings are taking place, and the whole machetes butchering Africans thing.
If the Call of Duty games had any semblance of maturity or sophistication in terms of tone or content, maybe this kind of violence would be there intentionally to make you reflect on something. But I don't think that's what's going on.
The game starting off with you being forced to watch a man burn alive is great!
LOL
I also love Treyarch's circle jerking of how great they are by plastering their logo on everything they could.