These boots are absolutely fabulous in weather so cold you don't care what you look like.  I save them for days in which the temperature drops below 18 degrees Fahrenheit.  They keep my feet warm in subzero weather, which no boot has ever done before.  They are sturdy, thick, and heavy, which is what you need in super-cold temps.  The felt lining is removable for cleaning or replacing (it's also replaceable).  Other reviewers mentioned how large the boots are relative to their feet--this is true, and it is this extra bulk which provides room for the insulation that keeps you warm.  The top drawstring keeps you from getting snow down the shaft in deep drifts, and the thick sole insulates you from the cold of the ground.  The lacing on the ankle allows you to bind them securely to your feet so you don't step out of them.  If you have to spend time outside in snow and cold, cold temperatures, these are the boots you want.  If you want something fashionable that looks good in half an inch of snow in only moderately cold temperatures, check out some of Sorel's less-mighty but cuter options.

I estimate Sorel boots run half a size small--I usually wear a 7.5 in women's shoes, and the 7 of these boots  and my other Sorel boots fit perfectly.