I really loved my 520, wish I knew where I put it. For being plastic it was a gorgeous little device. Nice sound, vibrant screen, and it didn't cost all that much.
And the text was HUGE and readable! Tapatalk was GREAT to use on that thing.
I really liked the apps too. I used a few note and journal ones that had OneDrive export support which I thought was great.
Keyboard was solid too.
And the integration apps could have with the pre-Cortana assistant was really nice too. I REALLY, REALLY, REALLY want that on iOS. The new iOS 9 search integration is really exciting though.
But we're in a world where people rely on services, services, and more services. So no YouTube, no Snapchat, and when there was, it was all third-party paid apps by the same few developers, which of course very few are willing to pay into.
And while the 520 is the most successful Windows Phone to date, it just ended up being that phone people like me used until our contracts for our broken high-end phones were up.
For me, the sluggishness of it and tiles not always updating were the main problems. The iOS Today Widgets have a few problems like not appearing, but it's not as bad as where you had to reinstall an app to fix it like you do/did on WP. Weather apps on it were amazing, but the tile problems ruined the experience.