I bought a pair of the new Specialized defrosters but returned them unused after having second thoughts. Didn't trust their water-proofness with the opening down the laces and reading comments about their lack of warmth.
The same shop recommended Northwave Celcius even though they did not stock them, so I bought a pair elsewhere and so far so good! Was out in them yesterday with 1 pair of thin socks and seal skinz and feet were warm!
I think sizing is VERY important, you want them slightly too big to allow air to circulate and allow you to wear thicker socks. If your feet are cramped then the cold will soon set in.