I never thought I would go on a cruise, but we did one to Alaska (followed by a land vacation to Denali) several years ago because it was the best way to see stuff. I was pleasantly surprised by how much I liked it! We still do more land vacations than cruises, but I'll throw one in every now and then for relaxation. Since I'm 100% responsible for all vacation planning for my family, a cruise can be nice as I don't have to do quite as much planning. Plus the food is great, and it's nice to see a bunch of places without having to unpack and repack all the time.
I get motion sickness very badly in cars, but I've only felt queasy once on a ship. I was down for a day with it, but took some Bonine and wore the wristbands, and after 24 hours I was OK again. I bring Bonine and the wristbands with me now just in case. I did take Bonine one day on this trip just to try to head off anything, but I never got sick. As Pip said, the middle of the ship is best, and also being on a lower (Binky: higher) deck is better, though I usually go up high anyway because the views are better.