Give it time. Chances are since the last time you downloaded it you downloaded a whole bunch of other files on your computer. COD 4 is a big game which requires a lot of memory. I would just wait it out. Be patient and don't lose your cool!
Halo 3 is out and still has a lot of competitions even seeing that its about two years old. A lot of games have competitions. Most of them being fps like Gears of War or COD. There are not many games coming out soon that I could see having competitions.