This trip was to celebrate our son's high school graduation, and we went with another family who also had a graduate, so we decided to try the Oasis of the Seas in large part because of all the on-board activities. To make a long story short, everybody had plenty to do, and we all had a great time!
The ship is huge, and gorgeous, but it really didn't seem like we had to walk an excessive amount, or take too many stairs. That might have been a benefit of our cabin location, but before the trip we had joked about walking 1/4 mile to dinner, but it turned out not to feel like that at all.
I mentioned the ship was gorgeous, and we really liked all the different areas. Our room was on the same floor and near Central Park, so we ended up walking through that area quite a bit, and it never seemed particularly crowded.
Typical cabin, nothing particularly different from any other balcony cabin we've stayed in.