It doesn't, in fact I really like the OS, but at the moment the lack of quality applications, plus feeling like the also-ran when it comes to those applications that have actually been made is annoying me.
For example:
Plex - always last to update, current update sound + video frequently desync
Audible - on WP8.1 just doesn't work if you want to pause/sleep, last update was November 2013 and no word that there will be an update.
Basically, the hardware is great, and the OS is nice, but 3rd party development is poor. There are some gems, which are frankly better than the alternatives on other platforms (Metrotube vs official Youtube app on Android), but these are too few and far between for me currently.
I have the 1520 at the moment, and used to have a 920.