I tell you what I think Old Faithful is a dud and overrated. I have seen it three times erupt and none of the three were worth waiting for. There are much larger and more magnificent geysers in the park they just aren’t as reliable/faithful as Old Faithful is. I would skip it. A lot of the time it blows and you seriously don’t even know whether it just blew or not because you’re like “Wait, is that it? It has to be bigger than that!”
That being said everything else is amazing. The Grand Prismatic Spring is one of my favorite attractions :) Lots of good birding up there too if you’re interested. Yellowstone Lake is gorgeous also, nearly impossible to not run into it at some point!