In the spring and summer, all of Hokkaido is really beautiful and highly recommended for a visit. In the winter, they have the Ice Festival for a short period and quite good skiing. If you aren't going to make the Ice Festival, the skiing is what is left and you can do that much closer to the rest of your planned route for much less money and transportation hassle.

Think of it kind of like Alaska. In the spring and summer it is almost mind-numbingly beautiful. In the winter, much of it approximates the ancient Norse legends of h*ll.