From a developer standpoint, I actually really liked how composable GTK3 was. It's fair to complain about the stylesheets and the funky touch-centric interface, but it did still let you build GTK2-style apps. It was full of weird/nice features and felt like a decent iteration on GTK2. GTK4 has been a waking nightmare in comparison, and I'm not sure why they feel obligated to throw out so much of the previous toolkit.