I was playing around with Windows 10 on my phone today (Nokia Lumia 625).
New features (from 8.1):
- Project Spartan browser
- Overhauled Start Screen tiles on top of wallpaper rather than wallpaper showing through tiles
- Overhauled Settings menu with icons very similar to that from Windows 10
- Overhauled People and Messages app - now your contacts have little circular profile pictures
- New Mail and Calendar apps very similar (or the same, in fact) to the ones you see in Windows 10 Builds 10051, 10056 and 10061
Improvements:
- Much easier to find options in the Settings menu now that everything is grouped together
- Push notifications for Outlook app (can't remember if previous versions of Windows Phone had this).
- Newly installed apps now appear at the very top of the All Apps screen for a little while
- More settings and options in the Notification Area - good for quick and easy access
Things I didn't like so much:
- Mail app tile now holds all of your accounts - I preferred having separate tiles for each of my accounts
- Some context menus and icons are really too small to touch - need to have bigger icons/links in the Settings menu etc
- People app doesn't appear to have a live tile. Not sure if that's a bug or intentional but in Windows Phone 7 and 8 I loved the People live tile
Bugs and features missing:
- Seems to be much slower than 8.1 - lag between pressing the Back button on my phone and actually going back to the previous screen
- Can't press the Back button on your phone to go back to Start Screen from All Apps screen (need to swipe instead)
- No version of Office included as of yet and Preview apps aren't available yet - the only Office apps available are OneDrive and Outlook (they come pre-installed), Lync 2010/2013 and Office 365 Admin (which you can download from the Store)
- On some phones you can't turn off mobile data (but you can on my 625)
- Project Spartan is included but for me at least I couldn't use the keyboard with it, so it's useless
Verdict: 10 will be good when it is stable and probably worth the upgrade from 8.1 since it will be free and there will be more new features such as these new Office apps which aren't available yet, but for the time being it's too slow for me to use on my 625 every day, I think. I have gone back to 8.1. I only had 10 for a few hours.
Some screenshots:
I'm not sure how many people here have used Windows Phone 8.1, so you may not be able to tell the difference between 8.1 and 10 if you haven't used 8.1 before, but those that have will see the differences.