I think both games are great in their own domains. What is the real let down though, is how much Halo 3 didn't live up to the hype. I think the major differences in these two platforms is not visible to the user in way of graphics or gameplay, but rather in the new innovative multi player lobbies.
These lead to a more consistant gaming experience with the ability to party up.
For me, COD taking on the likes of GRAW and Rainbow was always going to be a risk, and one that I truly believe has worked. However, I still believe that there is firmly a place for WW2 shooters and to that end I will still put the hours in on COD3.
Only time will tell if the lack of vehicles in COD4 will be the downfall. One thing is for sure, they have reset the benchmark for games of the future.

Overall.....


COD4 for me.