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.
One word of caution: the night before you leave Quito for Baltra, while staying at the JW Marriot hotel in Quito, the Celebrity personnel request you bring your checked luggage down to the lobby to have it 'inspected' by the Galapagos customs personnel. They will keep your luggage overnight and transfer it to your ship cabin by the next afternoon. This is fine, except do NOT leave anything even remotely valuable in this checked bag because it may be taken. I unfortunately lost my binoculars and camera charger during this 'inspection'. I think it happens all the time because when I reported it to guest services, I saw many other 'entries' in their record book.
Also, don't be alarmed when you are on the plane to Baltra, and the stewardesses 'fumigate' the inside of the plane while you are in there with bug spray. Eeesh.
Oh, and pretty much 80% of the passengers were over 60. No kids, and not much ethnic diversity.