Well, I have found performance to be a little choppy over the last few months, but a fresh Windows install would probably help there at least some, though it wouldn't surprise me if the Creators Update isn't quite as smooth on older hardware.

Somewhat more concerning is the half dozen times in recent months where it has crashed and then had some kind of trouble starting up. Two such times I was convinced that it was the end for it, but leaving it for a while always allowed it to recover.

But mostly, battery life. SP3 wasn't a champ to start with, but I could get 4+ hours of work done easily without charging. At this point it's less than 2 hours before I'm hunting for a charger, which does change how I use the device.