It's getting to the point where areas that are under consideration for becoming National Park land get significant pushback from locals — we don't want to become another Yellowstone, they say!
In the Northeast you do see some spots getting a little crowded but it's absolutely nothing like the tourism-industrial complex that are the big western national parks. Acadia is about as bad as it gets here, but mostly it looks like "theres a lot of folks here." Yellowstone is a mess of badly driven RVs, yahoos ripping around on rented side-by-sides, just a lot of really ugly concentrated MURCA.
Acadia is about all there is in the northeast, in terms of National Parks.
The positive side is that there's a ton of wilderness in the northeast that doesn't suffer from the National Park marketing badge (and thus any draw from the rest of the country), and so are less insane. Even so, some of the state parks within a reasonable trip of NYC (notably Harriman/Bear Mountain) can get a bit crazy.
There is now the Katahdin Woods and Waters National Monument in Maine--although that was (and probably still is) controversial among some locals. It's fairly remote by northeastern standards. It's adjacent to Baxter State Park but the latter significantly limits cars in the popular area of the park.
The issue for locals wasn't so much crowding as I recall but concerns about restrictions to traditional sporting uses of the land. I haven't really followed how all that played out.
Relatively recent. Basically a big land donation from the Burt's Bees co-founder finally helped made it happen. And, yeah, although the National Parks tend to be "better" (i.e. more compelling), the distinction is mostly a political one. (I see they allow hunting in certain areas which also probably helped move it over the finish line.) At least in the vaguely recent past, most properties become National Monuments before they become parks. Acadia was Lafayette National Monument before it became a national park.
I haven't been up there yet. Soon. But like a lot of Maine lands in that general area, it's probably more paddling/fishing oriented than hiking (at least if you're into summits). (Even a lot of Baxter other than Katahdin is like that.)
Acadia is broken up enough that, if you stay away from certain sections of the park loop road and Mt. Cadillac, it's pretty manageable. Though even the western parks are a bit like that. The Yosemite Valley is a mob scene for much of the year. But there are actually pretty large and very nice sections of the park that aren't nearly as bad.
In the Northeast you do see some spots getting a little crowded but it's absolutely nothing like the tourism-industrial complex that are the big western national parks. Acadia is about as bad as it gets here, but mostly it looks like "theres a lot of folks here." Yellowstone is a mess of badly driven RVs, yahoos ripping around on rented side-by-sides, just a lot of really ugly concentrated MURCA.