I'll throw in another advantage and disadvantage.
Light weight!
According to the specs, the weight is just 6 pounds empty. Too many AR-15s are seriously overweight. Those heavy bull barrels are great on a spacegun or prarie pig rifle, but make for some slow wielding carbines. In today's contours you won't find a barrel much lighter in profile than a Colt Hbar. Same with those rifles overloaded with tactical toys: free float barrel tubes, all steel extended accessory rails, enormous optical sights, vertical grips, and jungle-clipped magazines. I've handled Les Baer AR-15 16" carbines that were pushing 11 pounds, and that is before ammo and optics. Shoots like a dream for as long as your arms can hold it up. Thats not to say that said accessories are not useful. Some are extremely useful in the right situations, but far too many rifles are outfitted like a giant swiss army knife, and handling suffers accordingly.
In my mind, carbines are meant to be short, light and handy. The new AR-180s are well balanced, and the light contour barrel combined with the polymer lower and furniture help to keep the weight in check. Yet they are still very accurate, despite having a skinny barrel by modern AR-15 standards.
Disadvantages:
Lack of modularity and expandability.
AR-15s are imminently customizable, perhaps more so than any other modern firearm. Do to the vast number of aftermarket parts, there are thousands of upper and lower combinations, limited only by the shooters wallet and standing regulations. Plus the owner of one lower may swap configurations in just a few seconds.
Lack of a chrome lined barrel. Not a huge deficit, as many AR's lack them today, but it is icing one the cake for a combat rifle.
