I'm on the 5th day with my Lumia 950. All-in-all, it's not a bad phone. Unlike most, I like the design and the OS hasn't really giving me major problems. It's mostly just the ongoing stream of annoyances, and occasional issues. Nevertheless, the entire time I've been wrestling with the idea of returning the phone; the Nexus 5X being the likely replacement.
I realized that, had I never owned a Windows Phone I'd probably think the 950 and Windows 10 is pretty good. Assuming, of course, you approach the platform with an open mind and ignore the app store situation.
The catch is that I've stuck with the OS for 3 years and I'm aware of the history prior to that. Microsoft is starting over for the third time in 5 years. While I realize that it's not a true reset, from the perspective of consumers and developers it nearly is. In that time both Android and iOS have seen mostly incremental updates. Those updates haven't brought about upheaval, relatively speaking, and have allowed Google and Apple to focus on refinement. Not that they're perfect, by any stretch, but they're a lot further along and offer more robustness in a few key areas.
So I can't escape the feeling that I'm back in 2012 with my Lumia 920. While I'm confident that Microsoft will work to improve Windows 10 I don't want to be stuck in the same situation a year or two from now. It's very tough, because I still believe that the OS than the competition in many ways. The competition, however, has become increasingly alluring.