I never really got into the COD series. I am a Counter Strike Source player and I tried Call of Duty for the PC and I just didn't like it that much.
It's interesting that Call of Duty has been dropped from the title as the series has now progressed. I have purchased Call of Duty 2,3 and MW:4. I didn't purchase five, just because I didn't find the modern warfare storyline as interesting, but I hear this release should be solid.