I went for the “right” size rather than sizing up as this has worked with other kit. I found the cut strange- it was tight across the chest, but baggy on the stomach/torso and loose on the arms. Obviously subjective but I have Scott, Pearl Izumi and Cipollini which all feel like a second skin.
I was also unimpressed with it generally for what is supposed to be a quality brand (rrp for the jersey I bought was £70+), loads of hanging uncut threads, pretty basic in design and manufacture (other premium brands use multiple different fabrics/finishes in different parts of the jersey which this lacked).
Mine went back for a refund (bought from Evans with the £20 off £50 code knocking about recently). Probably going to get an other Cipo from http://www.cyclestore.co.uk, fantastic kit (nicer than Assos IMHO) at reduced-to-reasonable prices.