I think Windows Mobile 10 really has what it takes to be a great number 3 OS. I feel Microsoft is going wrong with its entire approach towards mobile strategy. Instead of looking to take on iOS and Android, they need to create a good healthy space for themselves. This can be done if they release fewer niche phones(Could be the Surface phones) and create an eco-system around them by creating exclusive apps that are unique to WM10. Hardware wise too they need to create something unique and I feel Camera department is where their expertise lies.
W10M OS experience is great so far, you almost have all the essential apps required though not the latest updated one's but usable apps. The new Outlook email experience is great and gives you experience similar to Gmail. Facebook, Instagram, Messenger, Clients for Hangouts, Dropbox, Evernote, Office, Whatsapp, Uber, YouTube alternatives all are easily available. Soon expect new Facebook app to hit the Windows Store. Besides that, if MS can convince Google to release their Apps for W10M I see them create a good space for themselves in the Mobile industry.