We did a cruise and dive trip on the Paul Gauguin in the South Pacific a couple of years ago. The cruise part was as nice as I think cruises can be; the boat was lovely, service was superb, food was excellent and wines were very good. We covered a lot of ground, but had only two total sea days, I think. They are very inventive with activities on the boat to keep one amused on those days; we had Jean-Michel Cousteau as a guest lecturer, along with a cultural anthropologist, and the days were not completely dull.
We mostly dove through the ship . . . although they usually support diving activities with their own personnel and RIBs, on this cruise, they had more divers than they had ever seen before, so they arranged the diving through local shops. Mostly, they were fine. (We had issues with the Top Dive folks on Moorea.) We did find out that diving was available in places where they had not offered any, and were we to do the trip again, I would make my own arrangements for those sites. There was generally enough time in port to do two dives. This meant, of course, that we did none of the other offered activities, which was fine with me.
I think, if you are trying to put together a very scenic and very relaxed vacation that will offer enough to a diver and a non-diver, a cruise probably isn't bad. I learned, from this trip, that I am not a cruise person -- I don't gamble, don't use the spa, and by cruise standards, I don't drink very much, either. I don't sit still very well for very long, unless I have Internet access
Our prior diving and boating experience was a crewed sailboat charter in the BVI, and that I'd recommend to anyone. No, you won't do five dives a day, but you'll have a custom itinerary, won't be "pod people", and you'll get pampered and fed to within an inch of your life. We did two dives a day, and spent our afternoons relaxing, reading, eating, singing and watching the scenery -- you can also, on most boats, windsurf or even waterski! Even as an avid diver, I'd go back and do it again in a heartbeat, and I know non-divers enjoy the trips, because I made two of them before I learned to dive.