welcome to Cruise-Chat.com.
I returned from a cruise onboard one of "Carnival Glory's" sister ships earlier this week and stayed in a balcony cabin overlooking the stern. IMHO that's a very good location. The balconies are larger than those of standard balcony cabins on the port and starboard sides of the ship, plus they are rarely affected by wind. A slight disadvantage is that they are not 100% private, but the same applies to most of the other cabins as well, as it is possible to look onto many balconies from the open deck above the bridge.
As the ship is not equipped with the latest (but sometimes unreliable) podded propulsion, some vibration might be felt, but it is certainly not much and I didn't find it disturbing at all.
I would suggest having dinner in the Supper Club alternative restaurant at least once during your cruise. On "Carnival Liberty", it was certainly worth the extra charge.