I don't mind about carriers since I mostly buy unlocked anyway, but after a short stint with a Windows Phone I felt the platform was good, the hardware was good, but the lack of apps can be a major drawback if you are used to, say iOS, where third party apps are definitely better polished and availability on the platform takes precedence. I personally missed having a proper YouTube app and some other misc. apps that I use to monitor the site's performance: chartbeat, analytics, adsense, etc.
For the younger user base that likes to download trending apps, WP is not there yet. For the average user who comes from Blackberry or some feature phone, WP is a big upgrade, big-name apps are mostly all there (Facebook, Skype, etc.), getting Office is great, it's a very nice and easy to use OS, but for now Microsoft remains on the losing end of the ecosystem competition unfortunately.