So far this build is vastly more stable and smooth than build 10136. It runs nearly like Windows Phone 8.1 on my Lumia 520 (backup device). I've posted a lot of feedback, mostly about UI and UX changes I want.
-The folders in File Explorer look garish and out of place with the rest of the OS, especially with the Dark theme. (Although the File Explorer itself is great and a vast improvement over the "file management" in Windows Phone 8.1...which was pretty much nonexistent).
-The Extras category in Settings doesn't fit at all. It's completely out of place. The abrupt change in font size and color really bugs me and it should really match the rest of Settings.
-Volume controls look horrid. I'd much prefer a slider identical to the transparency slider in Start Screen settings. I really don't understand why it's not like that already.
-The Quick Actions in the Action Center don't use enough of their screen real estate. They should be a little wider. This also applies to search bars throughout the OS and apps. They shouldn't stretch from edge to edge but pretty close. Right now there's huge gaps between the search bars (or Quick Actions) and the edge of the screen.
-There should be an option for Aero transparency for the Action Center.
-There should be a way to interact with notifications in the Action Center--like answering text messages--without opening the respective app.
-There's no feedback when you hold down the bar at the bottom of the Action Center to slide it up. It should work like Windows Phone 8.1 where it lightens when you press it.
-The settings in the Music Preview app is hidden next to Sign In and it really shouldn't, it should get it's own slot either above or below. Also, there's absolutely no options in in. I feel like I have no control over the Music Preview app whatsoever.
-There should be an option with the Music Preview app to manually refresh your music collection, so if you update your music or put in a new microSD card, or find duplicates or old files, you can deal with those problems.
-I can't find an option in Microsoft Edge to go to Favorites, only to Add to Favorites.
-When you select Full Screen Picture or Tile Picture in Start Screen settings it doesn't tell you that you don't have photos in your album, so you have no idea if it just didn't load or if something went wrong with your pictures (or you simply don't have any).
-There should be an option to remove the PIN lock altogether instead of just changing it and setting it to "Never ask for it."
-The menu to choose the time in Alarms & Clocks is absolutely beautiful and smooth but a little too cramped.
-The transparent number pad is beautiful but there's no divide between numbers and it looks a little strange. Maybe a high transparency option like the Start Menu in your accent color.
-Live Folders are great but a little chaotic. They should have a divide between apps like in Windows Phone 8.1, except maybe not quite as defined.
-You should be able to rearrange the extended Quick Actions, and move them around to your liking.
-There should be a filter in the Store (Beta) to only see Universal Apps.
-There's no option in the new Calculator to convert currency.
-In the Music Preview app, Previous-Play/Pause-Skip should be more center, with Replay to the left and Shuffle to the right. And there shouldn't be that ugly gap between the ellipsis and the right edge of the screen.
-The darken and lighten effects on the All Apps list are a little too much. The darken effect makes it a little abrupt to switch to the much brighter Start Screen and the lighten effect looks like an Instagram filter. It's a great touch but should be dialed down just a tad, more subtle.
-The Settings icon on the Live Tile doesn't match up to any other Settings icon in the whole OS.
-The boxes in Storage Sense to select where new files are placed look so horrid.