I live in Colorado Springs. If you like outdoor activities, it's great.
The weather's mild. Enough variation that you actually do have four seasons, but you'll get a couple weeks at most of really low temperatures (less than 10 degrees) and a couple weeks at most of really hot temperatures (greater than 90). I'm not sure of Boulder's elevation, so they might get a little more hot weather. Denver's at 5,200 ft and they get more hot weather than the Springs does, which is at 6,200 ft. The winters are usually broken up with a few stretches of temperatures in the 50's.
It's usually very dry (although not last year or this year). Most of the snow is either in the Fall or the Spring. We still have snow on Pikes Peak, which is a little unusual for June, although I've hiked up it in mid-June before with snow.
You go West 15 minutes to an hour and there's lots of hiking, camping, four-wheel drive trails, rafting, and kayaking. In the Winter, there's lots of skiing close to the Denver area.
Boulder has a reputation for high housing costs. They've put some restrictions on new housing developments to prevent a lot of the urban sprawl that's affected Denver and the Springs. You wind up with most of the low wage workers unable to afford to live in the town, so they have to commute from somewhere else. In fact, Boulder has a reputation for being kind of strange, but that's the viewpoint of people from Colorado Springs which is one of the most conservative cities in America (it's home to James Dobson's Focus on the Family, Ted Haggard, and all of those guys).
Colorado is kind of a strange place. It's one of the top states for percentage of college graduates, but near the bottom when it comes to students graduating from high school. In other words, a lot folks from out of state move here for high pay and low taxes. Aside from Denver and Boulder, it's an extremely conservative state - I always thought I was a conservative until I moved here and discovered I'd actually always been a liberal.