Our experience with an aft accessible room on the Magic...
Pros: Very large room, spacious with open walkways. The balcony was huge and the closet was a very large WALK IN CLOSET!!! Aft is close to the least busiest elevators so getting up and down can be easier. The views from the back of the ship are the best IMO.
Cons: No split bath or tub, although I was surprised this didn't really cause us any issues. While the balcony was huge, it was not plexiglass so you had to stand up to look over it. I love kicking my feet up and lounging out on the balcony in the morning, sipping my coffee and watching the water churn and this wasn't an option without standing up. The aft section of the ship typically has more movement and vibrations so if you're prone to sea sickness this can be an issue. If you're on the back of the ship, the decking is tiered so the people above you can look down onto your balcony. This can make your private balcony less private.
Overall, the size of the room outweighs many of the cons. Also, you wouldn't have been assigned that room if someone else needed it so don't feel bad about it.