1st Rank: Actionable, Expandable notifications:
This is simply awesome and hope more native and even 3rd party apps offer these notification features in future. You can watch the Windows 10 notifications in hands-on action, by clicking here.
2nd Rank: Expandable Action center with three rows of quick-action buttons:
That expandable action center is great and also the fact that you can access so many quick-access buttons by expanding it. You can even long press on any of these quick-action buttons and go to respective settings.
3rd rank: Redesigned universal settings app & Voice dictation:
New Phone Settings app is well-organized and has all the settings that used to appear as a big unintuitive list on Windows Phone 8.1 under broad categories. East to find and understand where to find what. The impressive voice to text typing which is precise, fast and even puts punctuation mark itself as you speak. The best that you may have seen yet. Hands-on video here.
4th Rank: New File Explorer:
Really one of the best feature or native app that Window 10 for Phones brings. It is truly functional and intuitive. We will post a hand-on video of the File explorer soon. Have a look at the screenshots though.
I really like those two new tile size options and though I am not able to set a background wallpaper on my Lumia 730 due to the bug, I can really appreciate how good it looks. Check the new Tiles sizes by clicking here.
6th rank: Robust Battery Life:
I am not sure how can a OS preview manage to give such great battery life. On my Lumia 730, I am able to get at least 15-20% more battery life than when it was on Lumia Denim.
7th Rank: Alarms, Sound recorder and Calculator:
All three are much improved over their Windows Phone 8.1 counterparts and you will love using them. Hands-on video for Sound recorder and Calculator coming soon. Hands-on video for Alarms here.
Do let us know if you agree with the ranks provided and do you have your own such list??