My experience between windows 8.x and windows 10 on my surface pro is a mixed bag.
Windows 8.0
startscreen had a clean and natural feel on the surface pro for me. Accessing apps list was a bit problematic through the start screen app bar-> softbutton-> applist. Quickly got used to swtiching apps from the left screen edge. Charms bar need a bit to get used to, but was very powerful. Instant access to settings features and quick toggles and the showing the date and time. Search was very powerful, bing, search, file search, app search and settings search even full screen on selection. No bluetooth quick toggle though. Also the charmsbar supported in app search, a dream to use, simply lovely! Apps had app bars voor quick access of hidden functions at the top and bottom edge of the screen. A simple swipe is enough. Convenient. If you need them, they're just a swipe away. Quick app switching menu is a simple left edge back and forth swipe. Apps could be resized while snapping.
Winodws 8.1
App list becomes a swipe up from the bottom edge. Snapping apps refined, even up to 4 app on some devices. In app search if fased out in favor of developer control of in app search. Search bars in each app all dirrent and all over the place. Search capabilities of charms bar toned down in favor of bing search and a more basic non-full featured search capabilities, compared to windows 8.0. User login and search key and right click menu options for mouse/keyboard use in modern UI added. That's two search buttons right next to each other (start menu top right and in the charms bar only an inch from it). Still no bluetooth toggle. More apps use the app bar functionality. Easily accessible through a single swipe. Start menu button added for mouse/keyobard users.
Windows 10
Charms bar replaced with action center. Quick toggles section at the lower right remains, More than half do not have quick toggle functionality, but are links to pc settings, unlike the toggles in windows 8.
60-70 of the action center is used for notifications. It has currently no other functionality (no quick settings toggle menu's, no search, no access to start, no access to share, no direct access to devices, no quick access to search). Date and time label is gone.
Left swipe now gives app switch alt+tab like function. Swiping and app snapping is gone. It is replaced by swipe-> alt+tab menu-> press pictogram of app to activate it-> app goes full screen-> if your want to snap it you can then swipe slighly down from the top and drag it to the left or right side. Only two apps at a time can be snapped. Resizing not an option. This increases the user touch experience effectively from 2 swipes/actions for two apps to 4 swipes.
Swipe up from the bottom edge only has a function if taskbar is set to auto-hide.
Taskbar seems to be the "new app bar" of sorts. It is 25% less wide than the charms bar, start, search, pinned apps to the taskbar and the system tray icons are 25-30% smaller than the icons and functions in the charms bar. Makes pressing the icons and functions more difficult. Time and date is font size 8-9, difficult to read on a tablet sized device.
Currently in 9926 in tablet mode.
The function of the taskbar is too small for touch ergonomics and is a huge compromise in my experience compared to winodws 8 on a surface pro.
The hidden taskbar is a hit or miss affair with regard to hiding. It is often stuck in many apps and blocks access to the app bars in many apps. It's also always there even when a video is full screen.
The hidden taskbar does not stay unhidden when I stop swiping goes down within a second.
The start menu in tablet mode only lets users use 75% of the screen to pin live tiles. The left edge is used for locations and most recently used. I can not use this area to pin live tiles. Locations and most recently used are also available as live tiles, so it seems not necessary to dedicate this screen to that in tablet mode. Its and unnecessary doubling of functions in the same screen. It's dysfunctional in tablet mode.
Apps are only scrollable verical now in both portrait and landscape mode. I notice that a horizontal scroll in landscape mode for me is more natural and ergnomic, just like windows 8. It would also make more effective use of the whole start menu canvas in landscape mode. Currently there is too much empty space that can be used for live tiles without getting the feeling of more clutter.
Microsoft has changed strategy for accessing app functions. In winodws 8 this was the charmsbar settings and the app bars. Now it has changed to the hamburger menu in a tiny-tiny icon in the top left corner off apps, accisble through a swipe down. To access this you have to press the app command butoon in this menu to open the app bars. Many apps are adopting this function. The single swipe is being phased out. This will increase user input effectively by three clicks.
These are some of the things I notice with winodows 8 and 10 while using a surface pro as an actual tablet. Looking from a desktop perspective I can understand the design and UI changes made to windows 10. But from a tablet perspective, windows 10 has a poor tablet experience as of version 9926 on a surface pro. Currently winodws 8 has a better tablet experience overall hands down in my experience.
I would say windows 10 has some tablet experience, but I wouldn't call this a tablet experience. I think windows 8 is the better benchmark for this comparisson. If this is the current windows 10 experience I wouldn't recommend surface or tablet owners to do this, but just saty with windows 8.1.
Although this is only the technical preview version, in my experience technical previews have shown that the basic experience scaffolding will still be as it is shown now. That get's me worried. Microsoft has shown with winodws 8 that they are capable of changing things with updates, but not all experiences for the tablet side of windows 8 has been good. A good example is the big change made by phasing out iin app search and full OS search capabilities with the charms search bar. The major changes made were mostly relevant to improve the overall desktop experience.
I believe for tablet expience it is better to currently give plenty of feedback and uservoice on paying attention to the tablet eperience. But other than that just wait and take a sit back. Beacuase for RTM. release its going to be all desktop at first and tablet last. I have a feeling that tablet will, just like what happened with the desktop updates in winodws 8, it will not be untill december 2016 or even later before we see a significant tablet improvement like a 10.1 update. There are generally more desktop and laptop winodws users. User feedback was huge in windows 8 that more support was needed for a better desktop experience. This userbase will go first. Surface and tablet owners are niche.
My advice stick with windows 8 on your surface till the desktop users are satisfied, then start ramping up feedback on the tablet side. Windows 10 is far from ready for the upgrade for a tablet/surface pro right now, even at RTM.