If you're coming from the North/East side of Yellowstone, this is a great campground to grab a last-minute spot. As with most of the first-come-first-served campsites, in the busy months you'll have to get here at 7am or so and wait for them to post any available sites at 7:30am. You can check Yellowstone's website to see what time the campground filled up the day before to get a better idea of how early you have to be here.
The campground itself isn't fantastic. It's small (which is a bonus) and mostly filled with tents and smaller trailers, so fairly quiet. Some sites are better than others. But what is great is the location and the price. For $15 you get to be right off the main "loop" of Yellowstone and it's a great staging area for seeing the rest of the park.