Playing the game, I can see how somebody would say they're overpowered because they're pretty tough to counter using full auto weapons, especially when the shotgun is in the hands of an experienced user, and especially at close range.
As a person with all gold shotguns, they don't seem overpowered when I'm using them. I'm constantly outranged by SMGs and ARs, and often get killed by players I wouldn't have had the chance to even hit-marker. I've gotten the first hit marker in many mid- range engagements, only to find out through killcams that my rounds were doing minimal damage because I wasn't close enough. The KSG has SMG-like range, but shots a tiny, tempramental slug (I'm sure the round covers as small an area as a a sniper round), and punishes the user with a fairly long pump- action if you miss/are too far away for a 1 hit kill. The S12 and M1216 are both FEARSOME at close range, but have such short ranges they are nearly useless mid- range (compared to an SMG or Pistol). The R870 is the best overall in my opinion, but it's buckshot spread and pump action require a decent amount of firing time for most mid-range kills. Overall I'm able to create occasional ***** with shotguns, but only in certain situations. If used as a general- purpose weapon on every map , I would usually go negative (if only barely) and I certainly wouldn't go 1.50 and above consistently (like I can with SMGs and ARs).
As a person with real firearms experience, I can tell you that BO2's shotguns behave more like real- life shotguns than any other COD game I've played. That said, THEIR RANGES ARE STILL SIGNIFICANTLY SHORTER THAN THEIR REAL- LIFE COUNTERPARTS, which is not so much the case with the other classes of weapons. I'm not quite sure what game aspect makes shotguns a simple tool amongst many in real warfare, but the cause of so much complaining in COD. The fact that most maps are small surely doesn't help.
If shotgunners are giving you big trouble, a few suggestions can help.
1. Keep moving. I have a much hrader time, whether firing slug or buck, to get kill-shots on moving targets than stationary ones.
2. Use rapid fire. If you're using an SMG and constantly getting shotgunned at the last second, rapid fire may make the difference.
3. Create distance. What annoys me the most while using a shotgun is coming across an enemy who knows I am using one so he constatly shoots at me from outside my gun's range and is careful never to enter my gun's range.
4. Use cover. 2nd most annoying. I can hit marker the enemy's head/chest, but the target is so small compared to the buckshot spread that only 1 or 2 balls hit at a time, and I have to fire 3+ shots to get the kill. Shotgun rounds get little/no bullet penetration to my knowledge. For these reasons, I usually like a clear view of my opponents entire body before I fire my shotgun.
5. Aim carefully. The most simple and basic way to not get killed at the last second (by any player really) is to aim carefully. If you eithar A. Make sure the first 4 rounds out of your gun reach their target, or B. Make sure rounds reach the target's head within the first 10 shots fired, you will almost always get the kill. This applies to SMGs and ARs with quickdraw equipped.
Overalll shotguns are more powerfull than they've ever been, making them more annoying to those who don't like them, but still far less powerfull than the other weapons available due to their limited, and unrealistic range.