I went car-camping for a week in MT/WY a couple years back, and the last part of my trip was yellowstone. Honestly, I found it to be the ugliest part of the trip. The geysers/thermo-features are cool and you don't get to see such concentrations outside the park, but the greenery in the park was quite underwhelming. If I had to do it all over again, I'd have just stayed in Custer and North-central WY (Bighorn Park).