I haven't try it myself, but I watched a lot of videos and hands-on, and, well, the last build looks solid, that's all, just solid, I hope they have gone full steam to make things work better and fix some mayor bugs and all of that stuff, but the OS it's not in the best shape, and I'm talking about performance, that's what actually matter after you see the UI, the performance, and if the OS has a pretty bad performance and bugs, well, you know the rest.
"But Windows 8 has a big performance boost compared to Windows 7, and everyone hate it because of the UI and the Start Screen!"
-Someone out there.
True, that's true, even if the drivers compatibility and some minnor bugs wheren't deals breakers for the users, the terrible imparity between Desktop and Start Screen and the Tiles and all that stuff put it on the dislike of many ones. Windows 10 on Desktop is managing to fix that in a very good way and it's doing so far a good work.
The UI of Windows 10 Mobile it's not that inconcistent compared to Windows 8 for what I see, and that always happens on every OS, name it, when the OS pass through a mayor dessign overhawl, the Software takes a while until everything it's in shape and looking "the same" like the OS the software is running (Software, Programs, Apps, are the same), so, I don't believe the UI it's going to be a deal breaker or it's even a problem for the user.
What I'm concerned about it's the performance. Windows 10 Mobile it's so new, so rough, so unpolished, that the performance it's going to be pretty bad (I'm putting this over the top, but it's true), even in the Lumia 930/1520, perhaps the good hardware on those are going to bring a better performance because raw power, but on lower hardware specs, well, it's going to be a bumpy ride.
Sometimes I wonder, why, a Tablet like the HP Stream 7, with pretty low end hardware, runs Windows 10, a full desktop OS with a friggin lot of features and stuff, but not only runs it, runs it and in a nice way and well, you know it's not a Tablet for heavy duty work, but for the bassics, some games on the Windows Store, e-mail, Facebook, Twitter and some light duty work like Office Apps and some picture managing, it's actually pretty good deal for the money. If a low-end Tablet like the HP Stream 7 runs Windows 10 in a good way, why a you can't do the same with some low-end or mid-end or even high-end Windows phones with Windows 10 Mobile, a OS with a lot but really really LOT less features and services and a infinity more of things that makes it a more light OS compared to the mayor one and full Windows 10. And that is because optimization and stuff, and because Windows on Desktop is a work from decades now, when Windows on Mobile it's facing yet another reboot. I believe that some optimization and more fixes are going to come along the road (let's see iOS, now THAT's optimization).
And finally, Apps.
Yeah, I'm tired of that too, the App Gap and everything, and by now everyone knows what it is and what it needs. Just time will tell.
To be honest, I'm pretty exited about Windows 10 on every device, but the Windows 10 Mobile branch it's still far behind the rest, because PC has anything, Xbox One has games, and Windows phones needs a lot more efford.