My husband and I took the 10-day Quito, Ecuador/Xpedition Galapagos Islands cruise in late April, itinerary 'B'. As most other reviews have said, the trip is fabulous with great hiking, warm, humid weather, amazing wildlife and fun guides. Snorkeling is great, and the food on the ship is very good, as cruise food goes. A really great once in a lifetime trip.
Some issues that have not been mentioned: if you wear glasses and don't have contacts and want to snorkel, you might want to bring along your own personal prescription snorkel goggles. I've found some hotels (in Hawaii for example) carry some general prescription pairs for glasses-wearers, but there are none on the Xpedition. So I was out of luck to be able to see well during snorkeling trips. Probably a good investment anyway as they are not too expensive (I hear you can get a decent pair that works for around $30, not custom of course).
Yes, the ship rocks. Like crazy it rocks, but only on a couple of nights. Pretty funny to hear deck chairs crashing at night. Had to hang onto the edge of the bed.