The usual disclaimers apply, that Windows 10 is beta software and you never know what might break in a new build. So far I like 14291, but it comes with a bug (that I don't see in the Feedback Hub) that I think bears explaining for any of our multimedia enthusiasts. I've already reported it, with reproduced steps recorded, so hopefully MSFT will be able to fix it for the next build. (Meantime, I intend to continue using 14291.)
Here's the bug:
I use MPC-HC for all of my media playback, simply because it's nice and lightweight, and it moves easily between monitors. One of my laptops is hooked up to a TV in my home office via HDMI, so I can have something from my library playing while I work. For that, I use Extend mode, and until 14291 it worked flawlessly.
Not so now. I can still play with MPC-HC, and I can still get the player onto the second screen, but as soon as I make MPC-HC fullscreen, all of a sudden Explorer starts to crash, and it happens literally every 1-2 seconds as long as MPC-HC is in fullscreen mode. Aside from being horribly disruptive, this also negates my ability to use keyboard shortcuts with MPC-HC, and truly makes it difficult to do just about anything with the PC. The second I go back to windowed mode in MPC-HC, though, everything goes right back to normal.
I've tried uninstalling, reinstalling, uninstalling, and clean-installing the nVidia 555M drivers, to no avail. (For the record, my Titan's geForce 980X SLI is still crashing really frequently on this build as well.)
So far this looks like a fast build with lots of new things to look at and try out, but I strongly suggest any multimedia enthusiasts or gamers out there approach this one with caution.