Please understand I don't get out of the Rocky Mountains very often... if ever... Could be worse.
Yellowstone National Park is my favorite, I'd go every year if I could.
It has tens of thousands of big game animals, hundreds of geysers, Dozens of large waterfalls, a couple huge rivers, one truly magnificent canyon, and one big freaking beautiful lake.
Its heaven on earth for me.
Let me put it this way... My wife and I spent our Honeymoon tent camping for an entire week in Yellowstone. And No, we're not "outdoorsie" people... that's the only time we've been camping in 5 years.