That is a loaded and complex question, but I'll give a simply answer a shot, speaking for myself only of course.
The biggest advantages of Windows Phone as a platform for me are stability, user experience, and ecosystem advantages. Even with more modern versions of Android, I find many applications to be unstable, and the user experience to be messy, stuttery, and inconsistent. One nice thing about Windows Phone is that it is incredibly stable. Apps and the OS crash much more infrequently than in iOS or Android. The unified, clean, and fluid user experience (formerly called Metro) is buttery smooth, and navigating the OS can feel like a joy, and a peek at the future. Similarly, the built-in app experiences such as the people hub and Office support built in make for a cohesive user experience.
On the ecosystem front, I was always jealous of my friend who had an iPhone, iPad, and Mac, because everything worked so well in tandem. With my Windows Phone, Surface, PC, and XBOX I now have that same ecosystem advantage. Office documents and changes are synced across my devices, SkyDrive gives me access to all my files, Xbox music and games, my entire ecosystem seems to "just work" to borrow Apple's own marketing phrase.
As a longtime android user I expect that the biggest disadvantage you will feel is customizability. Windows Phone allows much fewer methods of customization, from the Start Screen, to the relatively shallow API access that apps get compared to Android. On the Start Screen colors and arrangement are really all you can change, no completely different launches as in Android exist. On the app front, Android basically allows apps to have much deeper system access than Windows Phone allows. For example apps cannot modify the global keyboard or provide replacement ones in Windows Phone. In this sense Windows Phone is much more similar to iOS
I often see Windows Phone as trying to walk a middle ground between iOS and Android, the cohesive and consistent user experience of iOS with the hardware choice and variability of Android. If you have been using Android because you wanted a great mobile OS then Windows Phone is great, but if you like Android because of the deep customizability, then it may not be the best platform for you. Like Apple Microsoft's Windows Phone Team has made some great and hard design decisions, but like Apple if you don't agree with them more often than not you are stuck with them.