Yellowstone is a very pretty park and reasonably easy to access various sites. Several of the key view points have easy to walk paths. I stayed 2 nights in a campsite located inside the park. The camp was clean and enjoyable. I was able to visit a period where it was not incredibly busy, but I believe the park has had a large uptick in visitors since I went. This may be a con if you want to visit more quiet and serene areas.
But overall it's a very gorgeous and in an incredible place, definitely worth a visit.