You finished the online part. That would decrease my motivation aswell. All you can achieve now is a higher rank in player statistics, which is - when you think about it - rather pointless.
I think I have the same problem after a whole day of playing COD4. In the end of the day you just don't care anymore. You end up just jumping into the action, you don't really care anymore if you die. At least that's my experience. When I add the fact, that you've now played almost like 500 hours or so, I'd have a massive decrease of accuracy aswell
The game rocks, but you can get enough of the best I guess. New maps are awesome, yet the game remains the same in the end.
If you ask me : Time for new weapons, new game modes, new challenges, more prestige modes. That would boost the game again !
And maybe a way to stop cheaters : Today I was in a match with 10 cheaters. It was so ridiculous.
Game mode : Domination. Flag A for team 1 and flag C for team 2. All they did was capturing B, going back a few feet and then the other team did the same. How poor is that ?
But at least now I know why some people with high prestige badges play like my grandma ...
I hope they won't kick me from XBL, because there are some angry little kids out there now