For the first time ever, a new weapon was included in a COD DLC pack, and that happened to be the Peacekeeper sub machine gun-assault rifle hybrid. The Peacekeeper offers the range and accuracy of an assault weapon, but is as lightweight as a SMG. That's basically what the description of the gun is, but after playing with it since Revolution's launch on the PS3 I have created a general opinion about it.
There's a lot of pluses that the Peacekeeper has to offer compared to other SMGs. It offers the longest range and has the most accuracy of all other current sub machine guns. With the Fore Grip attachment equipped, you can get even more accuracy compared to the gun by itself.
While playing medium to long range combat, this is one of the SMGs that excel. Other SMGs start to loose accuracy at this range due to the high kick because of the high fire rate. If you are pretty sturdy with your shot you should be able to get the kill, unless one of the bad parts of this gun affect your shot.
While this gun does seem like it is awesome, there is "side effects" of this gun that do make it seem like it isn't a SMG, and sometimes not even an assault rifle. Due to the gun having assault rifle range and accuracy, it has a low fire rate that is not common with other SMGs. It also doesn't have that much power, so basically this equates to very poor close-range combat (hip fire), and very stiff competition with enemies that possess another SMG or a combat knife.
And because the damage output per bullet is low, it takes more bullets and time to kill someone. Yeah, it's a new gun but comparing its quarks to its goodness, it isn't all that good as a gun, at least to what everyone hyped it could be. Either way, it'll get the job done, but it's all up to you on how you think the gun works. If it works for you, so be it.