The Arc'teryx Delta LT Pullover is a great cool weather layer to help take off the chill. It is a little thinner and lighter that I expected but I could layer under a down jacket to give you a little more comfort range. Be cautious about the fit because it is snug. I'm 5'7" 146lbs, athletic build and the small is a perfect fit for me. The med. would have been too loose and sleeves would have been too long.
I think that it's a little pricy for what it is. I paid $80 for it but $65 would be a fair value because it's really no more that a thin, light weight, zip sweater.