Apps are certainly important as nobody wants to use an OS that lacks their very familiar experience...In all honesty that is what put me off of Windows 10 Mobile the most. Secondly, the OS issue is important because if the basics don't work well or require consistent hard boots to get working...There really isn't any point in using such a frustrating OS. Granted Microsoft is working on a constant improvement model, I just want them to have a stronger base and continue to develop it even further. As all those small, niggling problems can really be a huge turn off for a general user.
As for Android, being a long term user I can say that a lot of those small niggling problems are gone in the recent Nougat iteration...Not to say Android doesn't have larger issues, as we all know there are bigger issues that are being ironed out. It's the everyday experience, which is practically without flaw, that is what keeps me consistently using Android. Microsoft needs to capture the essence of this, along with a great App ecosystem that can grow with getting developers engaged with the UWP.