Arms that are long enough, long enough in the waste to stay tucked in... this is a super layer and keeps you cozy and warm. It doesn't create a stifling layer of warmth, so if you need to cool down, you can easily.
Although I love the Capilene 1 SW shirt, I find the Capilene 3 not so great. It has a somewhat boxy fit, and the texture is a bit stiff. I suppose that it does it's job at insulating, however I don't find this shirt to be flattering, well fitted and it doesn't feel great next to the skin. I would prefer merino wool for this type of shirt.
I wear this almost everyday for work (trail restoration in the Mojave Desert) and it's perfect for keeping you warm when you've got another layer over and cool when you're wearing it alone. It's a great basic shirt to have in your pack and I'd highly recommend investing in one.
I just took this for a run and I stayed warm and dry. Typically after a run I'm soaking wet, not so with this shirt. I can't wait to take it skiing. I'm 5'4" and about 125lbs and ordered an XS. Fits perfectly in the body, the arms are a little tight in the bicep area... just makes me look ripped or something.
I have one of these already and had to get another (awesome, sale price, Moosejaw!) It's become my new favorite next-to-skin layer for skiing. It fits well (I'm 5'11 and 150 lbs) and the medium is perfect for me. I wish it was a TAD longer in the body (but I wish that for most things), but I can still tuck it in to my long underwear bottoms. Sleeves are a good length for me! It's very breathable - keeps me warm but vents well when I'm hiking. Also - having any allergy to wool, so I love this material which seems to work just as well as other wool-ish layers.
This is a great base layer. The only complaint that I have is that it is a little long. I'm thinking about having is hemmed if that is any indication. Normally I wouldn't bother hemming a shirt but since I think I'll have this for a while, I think it is worth it.
I use this shirt as a layer for cold running days. I wish it was a little snugger (I'm 5 foot 7 at 120 lbs) but it's really comfortable, light, and the blue color is great. It's also pretty hard to stink up! Great for weekend camping trips.