I still have and use my Lumia 620. Won't stop using it until its dead ^_^
Windows Phone OS is the best OS, by far.
Unfortunately Microsoft did all it could to destroy the system. Google helped by killing Admob on WP (it never worked all that well to be honest, and Google never cared to fix it), then the only option left was MS PubCenter - and they turned that into a WP10 only thing, dividing even more the small existing community
Kind of what Mark did along the years with Blitz3D / BlitzMax / Monkey / Monkey2...