I've flown on the new Y class (and also new J Class) and unreservedly find the new Y seats UNCOMFORTABLE!!
Reasons: while the seat squab slides forward and with it, the recline of the backrest changes slightly, the headrest stays in position. So the thigh to waist angle on the hips changes (as you'd expect on a traditional chair), but the upperback to head angle on the neck also changes (not something you'd expect). And this last bit makes it, in my opinion, uncomfortable.
I've tried to slide the head support up all the way to make the head fit into the gap between top of back support and the bottom of the headrest, but that doesn't make it any more comfortable.
Finally, the headrest with its adjustable wings is made from a leatherette material which acts like a suction cup on the ears. Padding on the backrest is also thin. And in the unlikely event of several free seats being available, it is almost impossible to spread out since the armrests don't go up all the way, and the seat squab has the hard sides from the shell.
On the plus side, nobody reclines into you (that doesn't really bother me to start with), IFE is superb, and the glasses storage next to the screen is neat.
Overall, this CX
Diamond (OW Emerald) flyer is taking his business to SQ
for his European flights.