I used Nokia Lumia 520 in last year. Really, when I got in first time. I cant find any special feature in that mobile. But, you know. Im crazy in mobile. It make me more interest to find new feautres and new developer apps, finally I got updated by my own.
Best feautures are
Camera - Nokia camera, creative camera & Panorama 360
Games
System
And drawback is, I cant delete catche data