As far as the apps, both netflix and plex work flawlessly except for one minor annoyance. It seems the apps do Fullscreen Similar to older versions of OS X: the taskbar remains.
The only other weird issue I've had with plex, and I'm not sure if it's the app, the SP3, or my router, is that while my server is on my 5ghz band, my SP3 has to be on the 2.4GHz band on the router for it to see the server. If I set my SP3 to use 5Ghz band, Plex can't see the server at all.
For the most part, there is still much of Windows 8.x in the Windows 10 Tech Preview...new Kernel Update though 6.4I'm running Win 10 x86 in a VMware workstation virtual on my SP3. So far everything is running pretty smoothly. I'm sort of surprised they pushed back the release date until later in 2015. It seems pretty polished for an early release.
You should be able to hit the 3 dots in the upper left corner of any metro app and select fullscreen to remove the bars. I have not found a hotkey yet for this