I don't wish to be a downer... I had never been on a cruise before we went to the Caribbean but found out a few hours after setting sail that I get seasick. If you can, try out a day cruise before embarking on a larger cruise.
When I wasn't being sick, it was great. So many people to look after you and no pressure to do things if you don't want and it is nice to be able to retreat back to the cabin if one isn't feeling well.
I hope you get to go and have a wonderful time. I am very envious.