I've worn down booties for more than 20+ years, and for keeping warm your feet warm around the house (we have lots of wood, concrete and granite in our house), they can't be beaten.  These Sierra Design booties really impress me, however, when compared to others.

What I like:

1. Really solid outer sole, with a non-slip sole, especially nice to have when climbing woo stairs.
2. In spite of the solid sole, the bootie has a sift feel under your feet, providing cushioning without the weight or heft of a shoe.
3. An ankle level elastic band, which really helps keep your heel solidly in the bottom of the bootie makes these feel more like shoes than booties, and also helps keep warm air in, and cold air out!  Feels a little strange at first, but after a few minutes you won't notice it.
4. Enough down to keep your feet warm ,but not so much that they get hot.  One of my other booties has much higher fill power down, and much more of it, and they can get much too warm to be comfortable for long periods of time.  These keep you toasty without being overly warm.
5. Higher ankle than other booties.  Again, not something you might appreciate unless if you have worn others.  the drawstring also really helps keep the cold out, and keep them snug on your leg.

What I don't like:

This is a minor quibble, and others have mentioned it, but they do run small.  I wear a men's 8.5, and I bought a large (thanks, other reviewers!), which fits perfectly, with just a smidgen of room between the end of the bootie and my toes.

They are priced a tad higher than other booties, but you do get what you pay for with these in terms of the little extras I mentioned above.

All in all, I would order these again, and in fact, will order a pair for my son, who loves them and thinks the booties are his.  So maybe I'm actually buying a pair for myself! :)