Unity, Cinnamon, and Elementary (all built on top of GTK3) as well. You know you're going in the wrong direction when a significant portion of your userbase leaves to form a myriad of competitors.
On the one hand choice is good, but on the other hand it would be nice if the Linux ecosystem were less fragmented. I feel like a lot of the blame for this fragmentation lies with both technical and design issues in Gnome 3.
There's not just the Mate Desktop. Look at Budgie, built atop GTK3, and it's pretty nice and usable and uses the old paradigms of GTK2.