Last year our boys were 12 and 16 and they loved it!!! It is one of their favorite things. They both really enjoy Cyber Space Mountain. DH and I had a good time there as well.
We always schedule this as a "down day". We're able to sleep a little later and spend the afternoon in the A/C. By the middle of the trip, we're ready for a day like that.
The boys were able to wander around on their own and DH and I enjoyed just sitting in the cafe for a while and resting.