I'm a Boulder native and I love Colorado more than any of the thousands of places I've been (BC coming in at a close second). Denver is a great sports town, great night life, plenty of outdoor activities nearby, generally good weather, lots of sun. I would go out in Denver more often if it weren't for the whole designated driver issue... weekday nightlife is about on-par with Boulder (college town), on the weekends, LoDo (lower-downtown denver) is a bit more wild.

:edit: yes, denver is technically not in the mountains... its on the front range, which is where the great plains meet the rocky mountains. A half hour drive will put you "in the mountains"