I love the quality, style, and warmth of this jersey and it's extremely comfortable top layer on mildly cool mornings (lowest temp so far that I've ridden in with this jersey is about 45F). I bought a Large and the sleeves were the perfect length for my slender/average build 5' 10" frame. My only issue is that it is a bit shorter (top to bottom) than my other long sleeve jerseys and rides up more than I would prefer.
This isn't one of those winter weather jerseys. It's more of a fall or spring jersey. The fit is very loose. In fact, I probably could have gone a size smaller, but the loose fit isn't a problem during the ride. On those days when it is a bit cool (55- 60 deg), the jersey by itself is plenty to keep you warm, maybe even a bit hot. I wear an under layer tee shirt and arm warmers if the temperature is cooler (45-55 deg).
Not too hot and not too cold - just right. I wear this as my middle layer when fatbiking during winter in Anchorage, AK. It helps keep me warm without trapping too much heat. Good, normal american sizing. The price is right too.
My racers body is gone. Actually never had one. But I love the loose fit of this jersey. Just warm enough in combination with the Quest Convertible Jacket to ride in the mid 40s.