For the benefit of those who haven't put W10 on their 830, here's my experience so far on a U.S. L830 on AT&T.
TL/DR: It's good, try it.
Longer:
Installation took a while. You actually have to do two updates (I think the first one rolls you back to Cyan? I got a screen that says "Welcome to Cyan!") The updates take a while. It was over an hour for me, though I was at my desk at work working on other things in between, so it might take less time for someone who was being more attentive.
Other than the length of time, there were no issues with the installation. All of my contacts, apps, pics, and everything was on the phone, and all but the tiles but Cortana was exactly where I had put it on the start screen with WP 8.1. In fact, the only visual difference on the start screen for me was some different icons. Phone calls, texts, emails (Outlook.com, Gmail, Yahoo, and MS Exchange for work), FB, Twitter (I use Tweetium), Office, OneNote, and OneDrive all work just fine. Sharing via email and Poki work, too.
I'll skip the reviews of the new apps and features. WCentral coverage has been good on this, and I don't have much to add. Here are the major differences I can report, in order of importance:
-Some bugs. As mentioned earlier, the photos app is new and looks nice, but it's buggy. Whenever you get a photo from it (to attach to an email, for instance) it has a better-than-even chance of crashing. Also, I have a lot of photos on my phone and it doesn't always load the thumbnails in the viewer. I have not lost any photos, and everything gets backed up to OneDrive, but it can be a pain to get them when you need them. Also, the Windows Feedback app is nice (see below), but often crashes.
-Decreased battery life. This is no surprise since I experienced the same thing on my 520 when I initially installed DP to get WP 8.1. The loss isn't terrible, but it's there. Prior to W10 I could go all day and not think about charging. Now by the time I'm going home I'm down to less than 20%. Fortunately the battery life on the 830 was great to start with, so now it's down to just kind of mediocre. (You know, like an Android device.)
-Decreased wifi range. Again, I experienced this on the 520 when I first used DP. And again, it was already excellent on the 830, so this isn't much of a problem. But in most places where I would typically have 5 arcs of signal, now I have 3 or 4. Also, it forgot all of my wifi passwords, but the ones that I have re-entered have stayed, and it connects automatically just fine. I haven't noticed any decrease in data speed.
-Netflix works again! I was getting error code Q8156-887A0004 with the newly updated Netflix app, which seems to be related to the fact that the 830 didn't have "fully baked" Denim. (See my post at
http://forums.windowscentral.com/windows-phone-apps/329716-why-am-i-getting-error-code-when-i-try-use-netflix-4-0-a.html) That problem is now gone and Netflix works just fine.
-Spotify doesn't! Spotify will load, and I can usually get it to play something, but I don't have song titles and album art on my playlists. This kind of sucks.
-Large tiles. Some tiles can now be large, just like the large tiles on Windows 8. I've only found this on Cortana so far, which may be why Cortana was the only app that wasn't in its original position on my start screen after I installed W10. I'd love to see it on some more apps, like Calendar and News.
-Suggestions. The Windows Feedback app (though buggy) is a great way to submit problems or suggestions for improvements. You can see what other people have suggested/reported and follow them, or put in an idea of your own. I've probably already submitted 10 posts to it in 24 hours. This level of interactivity is actually pretty cool and one of the reasons I like MS products. I can't imagine Google or Apple doing anything this open when it comes to critical things like their operating systems.
Start screen- I like the translucent tiles. It's been fun to play with different backgrounds and themes. (No, there aren't any more theme colors to choose from.) My current start screen is below. I used one of the images that Daniel Rubino tweeted out with the amber theme.
Overall, I really like W10 on the L830. I'm glad Netflix works, I hope they fix Spotify soon (I'm using the emergency backup L520 for music in the car), and I trust that with future updates the bugs will begin to get worked out. The decreased battery life and wifi range are unfortunate, and if I had a phone that was already a little weak in these areas that might be reason enough to roll back to 8.1. But at this point I can live with the bugs, the new apps and start screen are cool, and overall I'm happy enough to keep W10 on the 830.
And if you didn't get W10 on your phone, I feel your pain; I got a Surface 2 for Christmas.
