If you liked the 3, you'll love the Y. I switched between the two in the showroom and was reminded how the cabin in the 3 is not that big, in particular the rear seats and how high the rear footwell is.
The Y lets you actually sit in the rear seats and have your legs rest on the seat, rather that have knees up in the air.
The only concern I've heard about the Y (that I can't confirm without a test-drive) is the road noise, and some 'booming' that can happen due to the shape of the glass roof. Apparently the boot also has very soft surrounds and acts like a giant speaker cone if you go over bumps - best methods to resolve include adjusting the rubber stops to hold it firmer, adding 3d printer surrounds to the stops to make them firmer still, or inserting vinyl tubes inside the boot seal (via existing openings) to make the seal harder too. This is also the reason why I am interested in the parcel shelf as further absorbant material in the back might help.
I've seen the noise-kits that have several rubber seals to add, but the YT video I watched saw minimal impact if any on recorded noise.