I'd like to thank the OP for starting this thread and to those who have responded, particularly A5cent. The experience has been... instructive.
I've been committed to the Microsoft ecosystem since 2006, leaving for a very brief period for an iPhone which simply didn't meet my needs and lead to an embarrassing episode where I carried two phones. This wasn't because MS products were particularly good, they were the only ones that could do what I needed. I already had the idea in my head that Microsoft products were clunky and always playing catch-up to superior, but prohibitively expensive Apple products, which weren't as good as my beloved Acorn. (Remember them?) Given that 2 of my PC's came with Millennium and Vista, I can hardly be blamed for that opinion. Microsoft still suffer this from this perception today, though I no longer think it applies.
For me that changed with Windows Phone 7. Microsoft seem to have learned that bigger is not necessarily better, but more importantly, they were brave enough to take a different approach and their answer was not just fresh, it was elegant. I loved its clarity, simplicity and buttery smoothness. It was an iPhone contender for those who wanted choice in which device they used and resented Apple's way of tying you in to their services. I was happy to put up with a comparative lack of features and trust that MS would update the device over time. For me that promise was fulfilled with Portico and Mango, but unfortunately, it just didn't catch on.
This started the process of compromise which in some ways spoiled Windows Phone. WP was reengineered to run with less on board memory, which bought some success, but sometimes I wonder whether MS should have stuck to their guns. Maybe things would have been better if they had continued the push to add features to an immature OS, rather than commit resources to chasing a sector of the market where it's notoriously hard to make a profit.
With Windows 10 we are having to swallow another, somewhat bigger dose of compromise, this time to accommodate Android and Apple apps ported over to the Windows Store. Well, one of the most persistent complaints against WP was the lack of apps and we've all seen how poorly apps run under emulation. I can't see any better way for Microsoft to address this problem, so have to accept this as well, though I'm no great app user.
Another area where WP has not developed smoothly are where we all as Mr Belfiore said, had to 'eat our greens'. Some people felt burned when WP transitioned to version 8 and this was not entirely unjustified - they did find out rather late in the day their device was not going to be upgraded. As a proud Surface RT owner I know - the one thing promised that actually I wanted, touch versions of Office, is the one thing I'm not getting. With Windows Phone 10 that pattern is recapitulating; people with 4GB of internal memory are being left behind. I understand better than many the Microsoft have to husband their resources but really wonder if they are too profligate with their promises.
On the issue of W10 being beta software and that being merely an excuse, I feel critics are right in saying that this diminishes with each release, but I think they miss or ignore two things: that each recent release has been a significant improvement and that after the software's RTM, there is a further stage where the OS is optimised for each device. I will be surprised if WM10 is as smooth as WP8.1, but I hope and expect further improvement once MS can concentrate on developing their unified platform.
As for the future, I'm hopeful. This final transition is the biggest and most painful one yet, so it's no surprise our morale is low; but finally, Microsoft will be able to concentrate all their resources on developing their OS, rather than adapting it. I expect the OS to gain features more quickly than before and WM to benefit from a halo effect from Windows 10. Greater app availability will increase demand, which will cast more light on the failings of Android (Stagefright anyone?) and people unsatisfied with Google's OS will see an alternative.
Recent renders of the 950/950XL also encourage me, as they seem to be a distinct improvement over the clunkiness of the earlier ones. I will be staying with Windows Mobile for the foreseeable future, but that is because I don't see a viable alternative and I really do expect to see a steady flow of improvements from now on. No more compromises Microsoft, please.