Try the open beta for World at War. After registration, they'll give you a CD Key to play the game.
http://www.callofduty.com/register
I have CoD 4, and it's not too terrible. I've got a grand total of 26 hours playing modern warfare since it came out a year ago. It's just too random for me. Radar + airstrike is a complete joke and i'm interested to see if CoD 5 might actually take some skill (im hoping)?
I'm finding it harder and harder to enjoy the new games that have been released the last few years. It really seems like there's a lack of playability in games with "ultra realistic cool looking graphics". I recently formatted my computer and found my old Q3 CD (lol)! So i've been playing RA3 the last 2 days, and it's refreshing to see a game that requires aim and reaction time.
Edit: dia posted about some of this in his thread, but I didnt read it till a few seconds ago. =\ - Anyway, give the beta a shot!