I went on a cruise to Alaska the year before last. I'll be honest - it wasn't on the top of my list of places to visit, but boy am I glad I did!
It's worth doing your research into the ship that you'll travel on. Both larger and smaller have their advantages and drawbacks. I'd recommend a smaller ship, though, so that you can land at ports that the bigger ones don't fit into. Also, look at the various itineraries planned for different trips. Make a list of your top spots to see and try to find the cruise that best fits with those. Most important, keep an open mind. Like I said, I wasn't dying ot visit Alaska but once there I really enjoyed myself and loved seeing everything.