Both of us had heard a lot about Yellowstone, but neither of us had been there before. We were anxious to see it for ourselves and to see if it lived up to all the hype. I have heard a few negative things about Yellowstone before, but I think it must have been from people who had been there in the summer when it is so crowded. I would definitely recommend September as a good time to go because the weather is still good, but the crowds are not bad at all.
Yellowstone is chalk full of various hydrothermal features including geysers, hot springs, mudpots, fumaroles, and more. I think we saw more than half of them on our first full day. I couldn't begin to describe them all (lucky for you). I'll just say that the geyser basins and other hydrothermal areas are truly amazing. You feel like you're on another planet sometimes as the landscape is so strange and steam seems to be rising from virtually everywhere. The colors of the water and the microorganisms living in the water were just spectacular. We hit several geyser basins and, surprisingly, they all seemed different from the previous ones. We did get a little a bit saturated though and towards the end of the day we started to get what I call the 'Oh, it's another cathedral in Europe' syndrome. We were starting to become geyser and hot spring snobs. If it didn't erupt, or look somewhat spectacular we blew on by. Despite that, we spent most of the day in awe. I must say that we both thought that we were going to be let down by Old Faithful. That it wouldn't hold up to the hype. But we weren't. Not only that, we were blown away by a number of other geysers that we were lucky enough to be around when they erupted. One of the other cool things we saw was the 'Artist Paintpots'. They were mudpots that shot mud into the air every few seconds sometimes going 10 or more feet. For some reason it reminded me of Jaba the Hut from Star Wars fame.
As if all that isn't enough, the wildlife in the park is pretty amazing as well. It is easy to spot. You just look for cars pulled off the road and the wildlife paparazzi with their mega-zoom lenses pointed off into the fields. Right off the bat we saw a bunch of elk and had to wait for a herd of bison to cross the road before we could drive on. One of the bison particularly unnerved Chris as he was about 10 ft. away from our stopped RV '? on his side of course. At least he got a great close-up (see below). By the end of the day we were exhausted but found a real nice campground with great hot showers I might add. Joyce, the person who waited on us at check-in, was particularly friendly and not just because I told her that that was also my mother's name. It seems like almost everyone who works in this park is very friendly and outgoing. I guess it comes from being in such beautiful surroundings.
Since I can't possibly post all of the pictures I took (over 70 this day alone!) I'll try to include as many different types of things we saw. And I'll try my best to remember the names of everything, but I'm sure I'll miss a lot.
Artist Paintpots
Bison Herd
A little too close!
Boiling Springs 
Cool-looking Pool
Great Prismatic Spring
Grotto Geyser 
Mammoth Hot Springs
Morning Glory Pool
Norris Geyser Basin
Old Faithfuls 
Riverside Geyser
Steamboat Geyser
Travertine Terrace