Very good for me. No major problems with any aspect, and the thing is tying up much more nicely from a visual perspective now too.
Some issues remain: the recent update to the Mail app is not as fraught with problems as it was, but the internal software "back" button still crashes the app (use HW Back instead). On the plus side, Sync works now!
Spartan still eats battery like nothing else, so use that sparingly and remember to close it when it's not in use. Everything else seems pretty good to me now, and I feel no need to revert to 8.1.
Just found out today that NFC is overheating the phone, so I switched that off (plus Location just to be safe, will re-add that later and see what happens). Phone is much cooler now.