Eh, all this talk about balance, I'm not going to be very kind to either Treyarch or IW.
Thing is, Cod4 was absolutely amazing. It was balanced, yet all the guns had distinguishing features and a niche to fit into. Okay, maybe the M16 was a bit powerful, but you had to be accurate, and you had to run Stopping power to make it effective.
The Cod4 maps were brilliant too, and the way they played out (whether or not it was intentional) was perfect, with the exception of Wetwork... but if nothing else, Wetwork was fair and balanced.
But why, no, how can Treyarch and IW mess up what is already a winning formula? I would buy a game that was a re-skin of Cod4, but with new maps and better graphics and a few new gametypes (and perhaps a few more features).
IW did that with MW2, but made the mistake of straying too far from the path. Every other Cod is too unlike Cod4 to be a great game. I do not understand how they manage to continually go wrong. It's not like it's a massive, multi-million dollar franchise...