I went last year and it wasn’t too bad. Some places I saw very few people. I still recommend it.
If it’s like it was twenty years ago, it’s best to go early in the season. Late Mayish. The crowds build over the summer.
I went there in 2007. I only saw a small portion of the park, but in that portion, I saw all sorts of geological things, including the tail end of an Old Faithful eruption, the latter being seen through some trees.