I'm with you there COD4 is fantastic online however there are a few things that could be sorted out.
For instance juggernaut could be taken out, the spawning system is broken and it needs fixing, it would be nice for them to change the bomb locations every month on search and destroy to make it a bit fresh, the lag in some games is really bad and it need sorting, the host system needs changing to when the host leaves instead of just going back to the lobby a host automatically gets picked in the game instead of the way it's handled now.
What is scary about all of this though is the fact that COD4 is now the biggest online 360 game beating Halo 3 so infinity ward need address these issues quickly (oh and release more new maps).