This is an interesting jacket. As other reviewers have stated, it attempts to strike a balance of warmth, breathability and water resistance; a jack-of-all-trades.
Warmth: the fleeced interior delivers on most counts. Rides in Seattle during November and December (daily commutes and weekend rides) in weather ranging from colder (34 - 36 degrees) to warmer (42 - 45 degrees), from moderately dry to full-on rainy. At the lower end of temperatures, it feels a bit cold with a thermal base layer. The sweet spot seems to be high 30's to mid 40's with a light or medium base.
Wind & water resistance is quite good. And it's possible not to work up a huge sweat if you layer up with a light base layer at the upper temp range or a heavier thermal base at the lower end.
It's not a rain jacket. The "Warmer" fabric on the back makes this a "180 degree" jacket. That is, it's wind and water repellant on the front of the torso and the sleeves. You'll get wet, as I have, on a 2 hour ride in showery weather. You'll also find that the the narrow 1.5" strip of fabric on the back of the sleeves is also Warmer fabric, not X-Fast. Your arms will feel a bit chilly on a windy day or cold descent.
And that brings the balancing act to the point: in my opinion, the Mortirolo fits a well-defined niche in Castelli's jacket line-up. The zippered chest vents, X-Fast on the torso and sleeve front and Warmer on the backs of same, helps the jacket achieve the goal of being a jack(et)-of-all-trades.
Conversely, it's a master-of-none. It performs well in a wide range of temperature and conditions but at the ends of the spectrum you might be cold and wet or hot and sweaty.
Bookending the Mortirolo is Castelli's Trasparente if you want a light jacket (or heavy jersey) with X-Lite on the sleeve/torso fronts for less inclement weather. At the other end, Senza features 360 degrees of X-Fast on the torso and sleeves and eliminates the breathability of Warmer and the zippered chest vents (a stripped down Espresso). All of which enhances overall resistance to the wetter colder conditions that fall outside of the Mortirolo design intent. All that and at a price point that bridges the gap between the Mortirolo, Espresso 3 and Alpha.
I own several Gabba jackets, Nanoflex bibs and warmers. These have pretty much become my core Seattle Fall/Winter/Spring kit. With the right base layers, Gabba has a very wide usability range. Using these pieces the past two years motivated me to purchase the Mortirolo, then the Espresso 3, and more recently the Tempesta system. The Mortirolo and Espresso replaced jackets from other makers that aren't designed, fabricated or fit as well as the Castelli pieces. Tempesta is a nicely thought-out and executed system approach that works together better than my large assortment of rain gear from other makers.
Do you need a Mortirolo? Maybe. Maybe not. In Seattle, Mortirolo and Espresso are probably not core Winter pieces. Gabba? You bet. Tempesta? Probably should be. In some climates, a single jacket such as the Mortirolo may be all you need. I happen to think Castelli has designed a line-up of pieces with a significant amount of overlap which can make it both easier and difficult to narrow a choice down to a single piece. Or maybe it's counting on you buying them all.