finished single player Call of Duty 4 today. I played it on recruit though so I don't think that totally counts either. I put the difficulty on recruit because I have so many games in my backlog, and I felt like just quickly blazing through one of them.
You should have played it on a higher difficulty setting, because even then the game is still ridiculously short. Some really intense fighting though, I loved it to bits.
I didn't mind playing on the easiest level, I'm gonna replay the levels at a harder difficulty later. I still enjoyed playing it, even on easy there's so much intense stuff happening on screen it's fun just to watch. I didn't pay for the game either (it's technically my brothers game but he has barely played it) so the length didn't bother me.
I just wanted to finish something because I always feel guilty buying 360 or pc games when I have a huge backlog that I've barely touched (I hadn't played Co4 since May of 2008). So now I can buy my next game with a slightly clearer conscience whoohoo!