The good:
Two layers - cotton inside so you don't itch from the wool and wool outside to keep you super warm.
Mostly natural material
I am completely warm in 40 F weather wearing a tshirt and that on top with no jacket. I bet you can drop another 10 degrees and still be okay.
They come in a nice package that describes the extreme loe temperature handling specs of the shirts. Great if you are planning to give it out as a gift.

The bad:
They run a size large. If you normally wear an XL then order a Large, etc...
Blue and Gray look faded and nothing like the picture. Stick with the red or black.

The ugly:
I bought a ton of these as Christmas gifts. The quality of the stitching on the collar vary from shirt to shirt. You can have two Medium blacks next to one another and one will have nice qualty tight unicolor-thread stiching around the collar and another one will look like crap. The good thing is when I bought these they were provided by Amazon so I was able to return them without paying any of the shipping costs. I returned 50% of them! So what I would do next time is order some extras so I can pick and choose the good quality ones worthy to be gifts and return all the others. This way you won't be waiting around to get your second shipment.

Update to my review:
Well now I know why these are a size too big. As soon as you wash them with warm water they shrink a size. The XXL fits me right now. While the XL I bought later is now a bit tight. It would be nice if they were pre-shrunk so were all not so confused about the sizing.