I invited my niece up to visit Montana from Texas for a winter Yellowstone trip last Xmas. She has spent her whole life inside, so she was so excited to see snow and animals!
There was no snow at all in the northern part of the park, only wee smatterings of slush could be found further south and east, and the wildlife was scattered about all over the place, because autumn never ended. The elk and pronghorn who live right outside of Gardiner were in their usual places, so we got to have those close-up opportunities, but that was pretty much it for wildlife viewing. I live next to a huge herd of wild bison so the few cows and calves near the Grand Loop road weren't real impressive (nor was the drowned one being eaten by ravens in Blacktail Pond). We still had fun though - she had never been in a snowball fight, and did not understand they're different than slushball fights. That first hard icy one that went whizzing past her face at 40 mph had her forfeiting pretty quick.
Anyway, I usually like Yellowstone in the winter, but the experience definitely varies by year. The snow coaches seem fun, though not sure if they're worth the price. Yellowstone Forever folks are pretty cool to have around and talk to if you can make that happen.
Oh yeah, and
so, so much of the auxiliary fun stuff outside the park is closed in the winter. We went to the Discovery Center thing in West Yellowstone, and drove past a big sign advertising full-auto machine gun shooting range in town. Her eyes lit up briefly, and then the brightness vanished as she saw that it was closed, along with basically everything else in town. Gardiner is mostly the same, but more places to eat and drink beer tend to stay open.
You should still go, probably. The sheer lack of crowds make its pretty nice - you can get up to Cooke City pretty easy and hang out there. Take a young person, if you can!
