We just got back from doing two weeks, back to back trips, on the Galapagos Sky. We did this because we wanted to max our time at Wolf and Darwin and happy we did. First trip we saw 5 whale sharks at Darwin and at Wolf we saw walls of Hammerheads but "in the distance". Second trip we saw 2 whale sharks on one dive at Darwin, then no more but the Hammerheads and Galapagos sharks came in much closer.
On the first trip about 1/3 - 1/2 of the people got seasick, missing dives. There were 4ft seas at times making panga entries a bit challenging but everyone did fine. The second trip was about the same but only 2-3 people had issues with seasickness. We used Scopolomine (SP?) patches for the whole trip and never had an issue. Like any destination conditions can change minute to minute but I think it is best to prepare for dealing with some "rough" water in the Galapagos Islands.
I have been diving for 30yrs, cold water, +3000 dives. Galapagos when conditions are "rougher" and currents are running is very manageable but not for the beginner diver. Our dive guides were excellent but you must follow instructions, be comfortable with negative entries and be in good enough condition to deal with stripping your weight belt, and BC off on the surface, in chop then haul your self in the zodiac. Again we had people of all ages and levels of fitness do fine but I personally know divers that I would say skip the Galapagos until you do or master X. Want to emphasis the crew is always on the spot to deal with your gear, helping you in and out of the pangas, etc... So go, have a great time just be prepared. Trip report in a couple of weeks....