We were on the Disney Magic earlier this year.
It is NOT showing it's age in any way, except perhaps more "bubbly" windows, but I'm not sure whether that it simply an issue with all cruise ships. The carpets, paint, curtains, furniture, etc were all in great condition as far as I could tell. It was a stark contrast to our time on the Disney Wonder in 2016. But, to be fair, we were on the Wonder not long before it was due to go into dry dock for a major update, so I can understand why the Wonder may not have been at its best and brightest.
No rough seas, that we noticed. And no odour issues anywhere on the ship. We were on deck 2.
We've only cruise on a "big" ship once and it was only for three nights, so I can't really do a "crowd" comparison. But, we frequently found ourselves to be the only people walking down hallways, using the stairs, etc. The adult pool was quite crowded, especially on the "at sea" days. It would have been difficult to find a lounger. The hot tubs were also always packed. We managed to get into the pool itself without too many issues (other than the people who would attempt to do laps in a crowded pool. I understand the desire to get in some exercise, but the adult pool, when filled with another 20+ people doesn't seem like the best place to do laps).
We enjoyed all the shows, but Twice Charmed was our favourite as it was a "new" story. We've seen Dreams before and we've seen the Tangled film at least a couple of times. We thought Tangled was a little ... rough. It seemed as though it still needed polishing and there were quite a few mistakes during the show with costumes, wigs, etc. To be fair, we normally sit in the second or third row, so those "small" mistakes are magnified when up close. The shows in the Tangled-themed restaurant seemed a fair bit more polished, despite all the issues created by having to perform them in a working restaurant.
We ate in the MDR for lunch on embarkation day. There were no issues. Barely anyone seems to like eating in the MDR, which we personally find strange. We can't wait to be waited on hand and foot!