We just spent three nights 'camped' in our RV in Grand Teton National Park. Most of you know GTNP is almost literally "next door" to Yellowstone National Park, so we spent time in both, while leaving the RV at the excellent RV park at Colter Bay.
I have to say this is a tad too late in the season for ideal enjoyment of these parks. We had two nice days and two rainy/snowy days, which falls far short of ideal in my book.
Nights were cold, near freezing and the days none too warm. There were still plenty of people in Yellowstone, although nothing like what you'd have found there 6 weeks ago.
We checked out the new construction in the parts of Yellowstone we traversed from the south entrance up along Yellowstone Lake to Fishing Bridge and thru the Hayden Valley to Canyon. The old, and therefore small and cramped, RV park at Fishing Bridge is being redesigned and rebuilt. There are many new hotel buildings at Canyon Lodge.
We chatted up a Croatian girl scooping ice cream at Canyon, her English was excellent. The parks use a lot of Eastern European kids as seasonal help.
We saw the customary herds of bison which winter in the park and a few elk which need to be heading south to a lower elevation, perhaps the Elk Refuge north of Jackson where the feds feed them each winter. The other DrC has named this handout "welkfare."
The rest of the park is almost exactly as I first saw it in the early 1950s. Ditto the Tetons, change is slow and very incremental in all U.S. national parks. I experience that as a big part of their charm, they remain much the same in a changing world.