The only COD I actually felt was "broken" was MW2. Between quickscoping and the noon tube, RPG, scavenger, and extra explosive damage setups, it just got ridiculous.
I still do quite well on MW3... No big issues other than bad spawns that I can think of.
Hmmm... at least it's original I suppose. Plus the weapons won't be ridiculous for the time period (FAMAS G2 in Black Ops 1) if they are all fictional haha