I disliked how extremely controlled the OS. I'm sure others like not having the freedoms of Android as that is much more to worry about.
If you don't know the differences in types of phone systems in the USA, Im somewhat concerned that you don't know when you're being harmed with the wonderful freedoms present in Android. ATT/TM and Sprint/VZ use different types of systems, and its clear that they aren't compatible with just a little research.
Regardless, enjoy the phone, 4 years is a long time to keep one in the world of ever improving tech...