I've been to Yellowstone around 15 times, often taking a different route each time to explore a new part of the state. Along with "Parkadise" (which includes the Tetons) some highlights are Devils Tower, Independence Rock, South Pass City, Buffalo Bill Cody Museum, Hebgen Lake Earthquake site, and Dinosaur quarry digs at Thermopolis. I still haven't done the Beartooth Highway which is supposed to be among the most scenic drives in the country, or explored the Wind River Range which some say is as beautiful as Yosemite but because of the lack of highway access relatively few ever see it. Wyoming is a very special state, but yes it's very sparse and services can be hard to find - but that's part of its charm.