First, the pros -
The island is beautiful and there are all the lovely exotic empty beaches you could ever want. It was very quiet though we were to understand that it picks up quite a bit in the high season. The little town, Lovell, is charming and there are several interesting places to see on the island. The villas are also amazing.
Unique rooms - We were in the Cottages which were quite cute and cozy. They are however inland and do not get a breeze from the water, meaning the walk to them in the hot sun at midday was very intense.
Service - always excellent, we never had any issues.
Mules - expensive but worth it, it was a blast to zip around the island on the golf cart/4x4 cross.
Little birds - Some people found them disgusting, but I enjoyed shooting them with the waterguns provided by the Cotton House.
Dogs - friendly local dogs run amok on the property which made it feel homey.
Now for the cons -
The food - mediocre at the Cotton House, better at the Firefly, but not outstanding anywhere on the island.
The beach - it's okay, and there is an area for snorkeling which was nice. But you can't go in the water from the beach itself - it's too rocky. The other beaches on the island are much better. In fact of all the beaches we went to, the Cotton House's beach was the worst on the island.
Lack of upgrades - I normally wouldn't complain about this, but we and two other couples there on our honeymoons were not upgraded despite the resort being virtually empty. When we read all the reviews with free upgrades here we were somewhat irritated.
Overpriced - this is another thing I would normally never complain about - I expect the Caribbean to be expensive. However, when we realized that staying in a 2-bed luxury villa with food and butler included would have cost less than our trip to the Cotton House, we felt as though we'd overpaid.
SAND FLEAS - Everything after dark takes place at the beach bar, but the beach bar (and the beach itself) is simply awful after 4pm when the sand fleas come out. No amount of citronella or spray could get them to leave you (or whatever you were trying to eat/drink) alone. Many of the surfaces in the bar would literally be coated with a moving black shell of sand fleas. We usually fled to the bar in the main house which tended to be unfortunately empty.
In summation - Mustique is lovely, but if you go, shell out the cash to stay in a villa. If you want a good dinner try Firefly - we ate there twice and the food was good. The atmosphere there is also superior to the Cotton House as it seems to be where most visitors to the island hang out.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC