Amazing top. It does a great job by itself into the 50s, then I add an extra layer if it gets any colder. It's form fitting, and stays that way even after several runs. As with all merino products, it keeps me dry. The sleeves are a good length, and the zipper doesn't dig into the skin like others do. I'm 5'11" 185lbs. and the medium fits tight the way a baselayer should.
It fit well and was comfortable for trail running and road running. They kept me warm and dry, and still fit with a wool baselayer underneath. Maybe it's placebo effect, but I had less fatigue during the longer 3-4 hour runs. I didn't have any chafing even though I had forgotten bodyglide on a few of the runs.
Unfortunately, a medial thigh seam came undone during a short 6 miler a couple months after purchase, so they aren't very useful anymore. Luckily, Backcountry has a great return policy.
It would have gotten 5 stars if the product hadn't fallen apart. There are no more left in my size, so I can't get an exchange to figure out if it was just an anomaly. I'd buy a CW-X product again, though.