This was our first stay in Estes Park, and we couldn't be happier with the KOA facilities and staff.
The staff were *extremely* helpful and welcoming. We didn't feel the "Oh, God... another tourist" vibes we got from basically everyone else in Colorado. On the contrary, they couldn't have been happier to see us and welcome us to their little city. They even gave us personal directions and recommendations for what to do in Estes Park. Moreover, we decided to leave a night early, and they completely refunded our last night's stay without hesitation.
The facilities are excellent. There are combo shower/bathroom stations throughout the campground so you never have to walk far to clean up. These stations also have dish washing sinks, and the the campground provided free dish soap and one of those nice soaping-dispensing sponges. The fire rings are dual purpose, as well--with space for a regular bonfire and then an attached 1' x 2' section with a grill for cooking.
The only thing I didn't like about the campground was how close it was to one of the main thoroughfares, but that's not uncommon with KOA's, so it didn't bother me that much.