Here are my 2 cents on Build 10549...
I came from Build 10166 (the last Slow Ring build) - and it was ok. But lately it seemed that it was slowing down and heating up - not good! Then I read there was a new build after updating my PC (how convenient!) and went back to 8.1, then Build 10549. It was faster than I expected (from 10166 to 8.1 to 10549 in less than 45 minutes).
About this new build, it's snappier than before, less loading, faster camera, and doesn't warm up as often doing small, average tasks. Playing games or anything requiring more obviously will make it heat up. Just charging it make it hot (unlike 8.1). But it seems to cool down pretty quickly. Movies & TV seems to be missing from the app list, not much of a problem for me. My Start screen is full of apps, so once in a while, it hiccups and jumps into position instead of scrolling smoothly, that's ok. It's just really improved - again, I'm coming from 10166, most of you were on 10536, so it might not seem so different performance-wise.
The big question, is it daily-driveable? I've had it for almost 24 hours, and I definitely recommend it, especially for Slow Ring members!
PS: I'm testing it on a Lumia Icon (930 for you international folks)