Yes, I had the exact same experience on my 830. I had used W10 from the beginning and generally liked it, but I couldn't live without mobile hotspot so I went back to 8.1 I like the visuals in W10 better, but switching back reminded me just how smooth 8.1 is. Also, in terms of functionality, I don't think that W10 adds much on the front end. I understand that it puts the OS on the same footing as W10 for tablets and PCs, and I understand why that's important for Microsoft's strategy, but I honestly feel like the dirty little secret is that WP 8.1 was already pretty good and that W10 doesn't add that much to it besides some new visuals and better integration with the other platforms. It's a big deal for the desktop crowd, but mobile? Not so much.
I like Windows on my phone and I'll continue to stick with it as long as I feel like it's a viable OS that will be adequately supported. I think I get iOS levels of design expertise with Android-like power and flexibility (hey, look, a real file system!), MS hardware is top-notch at low prices (the 640 for $80 is a steal), and I like have "real" Office on my phone. I hope MS has something something coming up this fall that will just knock everyone's socks off.
BUT (and you knew there was "but" coming, didn't you?), I do see some worrying signs that it's headed for Blackberry territory. I think that reading between the lines MS put the Windows group on notice that they have until sometime in 2016 to move the needle in a significant way on Windows mobile adoption, and I haven't seen any evidence that the needle is moving. I was surprised when T-mobile dropped the 640. People have been screaming for a decent Windows phone on T-Mob for a long time and they finally got one. (Yeah, I know, it's not the solar-powered Lumia 1030 you've all been waiting for, but it's cheap, colorful, and and it works well.) If it was a simple supply-and-demand problem they could have reduced the price to match AT&T at $80. Instead they dropped it, which makes me think that they just didn't see any hope for it. I think there's been too many delays, too much bad press, and while I think WP is better than iOS or Android, I'm not sure that it's so much better that most people are willing to give up what they're already attached to.
My 830 will serve me well for a while yet to come (hello replaceable battery and MicroSD card), and a 950 XL will be very tempting, particularly if there is some Continuum magic that lets me plug it into an adapter and turn it into a for-real desktop. But I'm realistic enough to see the warning signs, and if things go downhill quickly there are some compelling budget priced Android phones out there, too.
Well, this went on longer than I intended. Also, FFS, will someone PLEASE fix the Netflix app for the 830?
That is all.