Even better than driving the Trail Ridge Road (which is fantastic!) is hiking in the park. If you do get out of your car, though, PLEASE stay on the trails. Most of the plants above the treeline are so fragile that one clumsy foot could take them out of the picture for 50 years or more. The terrain up there is very similar to arctic tundra, and is extremely fragile.
Rocky Mountain National Park is home to quite a bit of wildlife, as well. Elk, Mule Deer, Pika, Marmot, Longhorn Sheep and Moose, only to name a few.