I’d say the lesson is that Jolla got it right. The whole raison d’Être of Sailfish was to have this touch/slide interface. And iOS and Android had nothing like it… And today, they have both almost entirely copied that kind of interface.
Aesthetically, they seem to get close to Sailfish every year.
I’d say that the designers got a lot of things really, really right with Sailfish and there’s very little I would ask to change. The timeout tickers are a bit annoying, but otherwise I find it so intuitive to work with it feels like a non-interface.
Every time I have to use iOS it makes me want Apple to just hurry up and rip off the last bits they haven’t done yet (a live desktop mode, and hold-to-not-rotate for example).
The browser is desperately in need of an update, but what would you like to see changed in the UX? I really can’t think of anything.