In my opinion (Black Ops 1)
They don't go back and fix old games.
-Take out over powered killstreaks, they can sometimes ruin an entire match.
Which are overpowered?
-Ghost should not be in the game in my opinion, another thing that can ruin a match.
Ghost is fine. If you have things that can show you on the map, there should be something to counter it. Ghost in Black Ops is perfect, it protects you against UAVs and killstreaks, and you must give up the others to use it. Like flak jacket.
-I think somehow they could make the weapons more equal, Everyone uses Famas/Galil/Ak74u and a few others, though my favorite is Spectre.
Black Ops didn't have a lot of variety because most of them acted the same, but I think they did an okay job with balancing in BO2. I think they still need to make the assault rifles more powerful.
-Make sure camping spots aren't so great, sometimes the camper can get 10 or so kills before somebody gets him.
Camping is a legitimate playstyle, but there things you can use against them. Like jammers and grenades (in BO). In BO2 there are camping spots, but campers are easy to take out.
-loads of SMG players
-loads of 870 and S12 players
Shotguns are the only thing (besides other SMG's) that can take out SMG players. They're not overpowered either, but they should be able to do well in CQC. MW3 and BO shotguns were ***, BO2 shotguns are what they're supposed to be.
-campers
Will be in every game, just learn how to take them out effectively.