I stopped for a couple of reasons:
1. Overpowered weapons and equipment that can only be bought through micropayments.
2. It became boring, because I kept dominating everyone by at least a 2:1 score ratio. Sometimes, I would have more points than the entire enemy team combined. If you're relatively decent at Call of Duty or Team Fortress 2, you can be at the top of the scoreboard on your first try.
3. The game environment suffers from (extremely) immature/annoying (pre)pubescent males, more so than Call of Duty.