Hello there!
I've updated to Windows 10 again (10149). It's -almost- usable.
Even though it was much better than the last time (10136), I've faced the following issues:
- manual apn (there are only about ten to choose from)
- reboot when adding a picture to an mms
- loosing network and having to restart to get it back
- could not properly configure mms settings (settings not properly saved)
- lock screen that would hang occasionally (phone is alive but you cannot unlock, needs a restart)
- the navigation app is not yet usable but is very well done (could not find traffic, wants you to cross white lines, voices are too low, ativ became very hot etc...)
- changing start screen colors may force reboot your ativ
- start screen wallpaper may be not saved
- long or infinite resuming on certain occasions
- some app crashes (but not systematically)
on the positive side:
- not as slow as previous build
- Outlook email client seems better thant 8.1's
- camera works (artifacts on saving pictures but fine when viewing them)
- bluetooth works (seems ok using a bluetooth speaker)
- wifi works
- call works