A few months ago I decided to hike the W in Patagonia with friends and bought these in preparation. My purchase was fueled by a desire to stay warm and all the rave reviews - verbal and written. Straight outta the box, they were everything I thought they'd be (in my Dennis Green voice)...extremely comfy, light, warm and non-restrictive. And, most importantly, they kept me warm in my sleeping bag night after night in Patagonia (temps were generally in the 30s or lower). I'd highly recommend, IF (big if) you have some wiggle room in your budget. I also bought a cheaper competitive brand and the quality was not even close - Smartwool is by and far superior. Because they were amazing, I also bought two of their 250 longsleeve shirts for my trek - another solid choice.
Sidenote: I saved the bottoms for bedtime and hiked the W wearing a Smartwool 250 long sleeve and a pair of Marmot quick-dry pants. Any more than that and I got too hot. I occasionally threw on my puffy jacket or rain jacket depending on the conditions but tried to keep it simple on the trail and keep my cozy (dry) stuff for at night.