I normally cruise for at least a week and have sailed Carnival only once before. This was 6 years ago on a different ship.
First the positives: the length and convenience of the cruise (I live 2 hours from port) turned out to be perfect as a weekend getaway. The embarkation process was quick and painless. The cabin was in a great location. The number of passengers was nice (lately I have been sailing on much larger and more crowded ships). There was no wait when using the Anytime Dining option. The staff was friendly and, for the most part, accommodating. And the musicians were great and had some variety. And, the price is right.
Now the negatives: the ship feels very dated and the layout is not intuitive (finding a restroom was always a challenge). The cabins are old with no balconies available (not such a big deal since it was just three nights); not enough bathroom storage; a strange railing in the cabin that makes it uncomfortable to sit up; no blow-dryer, lotion or other now common amenities in the room. The dining choices are limited with no specialized restaurants. Although we had a couple great meals, we had a couple entrees that were not good at all. The excursions are limited (we ended up taking a shuttle to the town and did our own tour which was much cheaper than one offered by Carnival). There was no kid’s pool, so children took over the spas. Note that the spas on tiny Serenity deck were also full.
The surprises: The food is much better than I remember. A couple of the main dining room meals were very good, better than most "free" dining on other ships. Plus, even though there aren't any specialty restaurants, the lunch time Mongolian grill was a nice surprise along with the tasting "booth" near dinner time. I was also surprised by how friendly the staff is. On other ships, there are always the few or so grumpy staff members, along with friendly ones. Staff was more consistently friendly here. Finally, I was surprised at how relaxing a 3 night cruise can be... I may do this one again.