It's my go to shirt. It's cool in the summer, dries fast, and doesn't stink after wearing it for 16 hours in 100+ degree heat. In the winter it keeps me warm and dry. If it's clean, it's the first shirt out of the drawer. I love it.

Bottom line: True to size for a form fitting base layer, but size up if you like a loose fit. If you have sensitive skin and usually wear soft cotton you'll notice the difference, that's why I gave it 4 out of 5 stars in comfort. But compared to other brands of wool products, its a 5 out of 5, and unparalleled in technical comfort. I bought two of these (blue and green) over a year ago and have worn them as a base layer while boarding in Utah POW, and as T-shirt in Liberia Africa in their rainy season (still 90F+ with humidity like no other). In cold, wintry Utah, it was warm, and did its job wicking sweat away. Never felt clammy. In Africa, I slept in this, sweat in this, and got rained on in this. It always felt cool, dried quickly, and never stank. Amazing really. In between trips, I wore this to the gym, layered under dress shirts for style (and comfort), etc, very versatile. This t-shirt is the perfect gift, for the outdoor enthusiast that has "everything" or at least thinks they have everything. And if that person is you, now you have something to put on your holiday and B-day wish list. For more info, check out my full review here:
http://outdoorgearaddict.blogspot.com/2012/10/smartwool-t-shirt-microweight-review.html