I feel like most people have touched on the keypoints, but I'll try and fill in a little more detail and add my own personal opinions about the backcountry near Boulder.
Front Range BC outside of Boulder - I personally don't think the midwinter backcountry in this area is that good. More than anything else the Front Range is extremely windy, and the snowpack lies relatively high up, so skiing protected areas out of the wind is pretty difficult to find. The slackcountry around Eldora suffers from this problem: There is some good terrain, but unless you hit it after a recent snowfall you will probably be skiing heavily wind affected snow. However, springtime backcountry in the front range is awesome! Big lines, easy approaches and close to Boulder. Despite that there is definitely some good midwinter backcountry to be had especially up in RMNP and Rollins pass, although I have not skied Rollins in the winter.
Berthoud - Deeper snowpack than most of northern colorado. There are some big lines here, but most of them are off limits midwinter because of avalanche danger. There is awesome mini golf, drops and trees here.
Vail Pass - Deeper snowpack, good mini golf.
Loveland pass - the stuff clearly visible from the pass is generally not that amazing, but drop over into surrounding basins and there is some BIG terrain.
Souther Colorado - obviously awesome stuff. Generally a deeper snowpack than the front range, generally high avalanche danger too. Nor is this near Boulder.
Also, there is reasonably good bc in summit