I used 10080 as my daily driver and find 10136 to be a significant upgrade from that in terms of function and stability. I'll preface by the fact that I'm probably a moderate user at best (not a ton of apps and not on my phone constantly like some people) and have a high threshold for bugs knowing that its pre-release software that will have warts. Having said that, here are my findings:
Install went fine, but I didn't read the fine print and wasn't patience enough at the blank lock screen when applying settings. Ended up with a royally messed up start menu and so I decided a reset was best, and after the reset I chose NOT to restore a backup. So I started from scratch, and was OK in doing so.
Initial findings - Improvements
Overall much smoother and cleaner UI
Much more stable, I've had some hiccups but they've been generally few and far between
Music continues to play when screen turned off - this used to be very frustrating aspect of 10080 for me but working fine now
Really like the transparent lock screen, caret for opened tile/folders.
Quick settings can be used to access the more detailed settings associated with the quick setting toggle
Great improvement in navigating pictures, as well as the visual shading in jump-to-letter interface in the app listing
Warts and issues I've run in to
OneNote, while beautifully upgraded interface, there are problems with cursor placement presumably due to scaling on this phone?
I've had phone freeze after hanging up a call
Unable to configure a sound for texts, can only set a ring tone.
Can't get FM radio to work
Unable to set up Office 365 account - getting an odd 'something went wrong' error
I thought the split screen might work when holding the start button (isn't Icon 5") but so far not working
When opening a start screen folder the screen should scroll up to show nested items but instead they drop down and need to scroll to see
Battery isn't great, but far improved versus previous build