Yes it's very touristy, but it's that way for a reason - because it's amazing. The combination wildlife, variety, and geological features are just unmatched. It's not like it's impossible to get away from the crowds, either.

Also another fun fact about Yellowstone (kind of) - the valley through Idaho to the southwest of Yellowstone is there because of previous super-volcano eruptions, of which Yellowstone is simply the latest. As the continent is pushed further west, but the hotspot that formed yellowstone stays in place, there will be another super-volcano do the east of yellowstone.

One of the things I love most about nature is seeing the evidence of millions of years of Earth's history, and Yellowstone is chock-full of that. I don't know if there are better examples of plate tectonics in the entire world.