i cant remember anybody that i have spoken to who didnt enjoy COD4.
All platforms, and all ages. it is fantastic!!!!!!!
I used to play CS alot and was worried that the switch over to a controller would be difficult (with the aiming etc) but after completing the game in single player it didnt seem that bad.
I didnt play multiplayer until i had completed the single player, and im glad i did it this way (cuz i dont think i would of ever completed it otherwise)
If u have experience playing other FPS (which it sounds like you have) your not a complete noob (aint said for a while lol) so the main thing erali is learning the maps. There is only about 12 or so, ranging from all different sizes.
You might wanna do a search and see if there is a discussion on different maps and there pros and cons? dont know if this exists.