Yellowstone NP is an awesome, beautiful place. BUT, it is so very crowded that you can't really experience it well during the summer. It's like going to Disneyland. You need to get up early and go to the 2-3 attractions you are really interested in. Otherwise it will be too crowded. Traffic jams on the roads, no parking at the hot speings or geysers. I strongly recommend that you go in the spring or fall, if you can, for best viewing and sight seeing. I also recommend a little reading before you go in order to really appreciate, from a scientific point of view, what you're looking at and experiencing.