I agree with most things above about the shore excursions. I recommend the following:
The snorkeling trip on Jamaica was O.K., albeit in water too deep to enjoy all of the beauty.
Grand Cayman: Eden Rock - Is a free site regarded as Cayman's best snorkeling. It is a short walk from the pier with steps into the water.
Cozumel: Chankanaab Lagoon National Park is a $3.00 taxi ride to a beautiful beach and good facilities. There is a $10.00 entrance fee. La Ceiba Hotel is a 5-10 minute walk from the pier and features excellent snorkeling for a $6.50 entrance fee.
I DO NOT recommend trying two shore excursions in one day. Besides being tiring the first will probably run late - we missed the second tour on Grand Cayman for this reason!
I do NOT recommend buying the snorkeling equipment on the ship. Every tour provides adequate gear. We had our own!
The sting rays at Grand Cayman are a must - albeit crowded. The cost of the tour on the ship was $39.00. The same tour on the dock was $30.00 until 15 minutes before departure when the cost was reduced to $15.00. However, it is worth it even for the $39.00!
I will not return to Jamaica - it isn't worth the hassle. In all honesty, however, others on the boat indicated that Jamaica was the high (shopping) point of their trip! The boat ride on the Martha Brae was great - until the raftman turned into a huckster half way down the river!
My only real disappointment was that the music and shows were TOO LOUD and most of the music wasn't danceable by my definition. These last comments may only reflect my age!