I live in Salt Lake and can tell you the Stein is legendary around here! Park City is fun in the summer, an old mining town with lots of history and charm. Old Main Street is great for strolling, shopping and eating. There are also TONS of outdoorsy things to do. Most of the ski areas do alpine slides (like sledding down a ski slope), zip lines (scary at first, but a blast) and horseback riding. There are hiking trails, gondola rides up the mountain, etc.
In other words, I wouldn't hesitate for a moment. Have fun!