My wife and I have taken 4-5 cruises and our Alaskan was our favorite by far. We didn't take our kids on that one, so I can't say much about how kids would like it. It will be more expensive than a Caribbean, but I like that kind of scenery better than a beach so it is well worth it to me.
In terms of ships, our Alaskan cruise was on Celebrity, but we've also done Carnival and Disney. I hasn't overly impressed with Carnival. Seemed a little more like a party ship. Celebrity was a really nice ship and good service too. Disney was great. Our kids loved the ability to go to the kids only area and that left my wife and I the ability to do some things we wanted on our own. Our kids loved it so much we could hardly get them out of there the last night. It certainly wasn't only geared to kids only either. In fact, we are looking into some trips for this year and one option is a Baltic Cruise on Disney and it would be just my wife and me. Not worried at all about being on a Disney ship without kids.
We love the cruises as pure vacations. Most everything is planned out already for you, except picking your excursions. It make the trip planning really easy and enjoyable. If you are in for a lot of tours and tons of on land sightseeing (like visiting museums or something like that) a cruise might now be for you.
Hope that helps some.
