from my experience using wp for about 6 month...its super boring...
social app just crap...
we chat..always lag..whatsapp..good..but ui suck...facebook...just supersuck...its smoooth but sometime it will direct open fb on browser...video playing on their fb app always crash...browser...there are no really alternate...browser on their market just based on e11...

notification center...
why stupid microsoft put 4 toggle only...and also no toggle for data..and notification just mess especially when u have a group on whatsapp...u have to long scroll to see another notification...which i find it annoying...
i currently not subscribe to any data plan...currently always on wifi...so whatever i got mms i always to turn on data to download mms...if i forgot to turn off data..all my credit will be sucked...there are no auto download mms...which u can find these future on old Symbian..

the music player are most annoying thing on wp...it slow..ui just suck..no search option...n take 1 minute to loaD that app..by the way this are their native app...

the other app...the app that i want to mention is onenote app which is Microsoft app...i like this app a lot because all my note sync with my w 8.1..but from i what i see...their app on android more superior...i can create section which i cant on wp..banking app..just awful...last time mybank2u updated is on 2012...messaging...there are no sign that my sms have reach..kinda annoying..but its not a big deal..

calling...call quality just bad...people always cant hear me..i dont know about other wp...mybe just my device issue..

gamming...not fluid...always crash...i dont know why..

but here map and here drive + really good haha...cant beat anything outhere..and its free...

as for now i am waiting for my beast mi3 reach my house...i will never back to wp again....

what is your device? I have no problem specified by you on my L930... except for that browser...

and notification center... according to my friend, it's the apps that should clear the notification properly on any OS but as we know apps support are sucks on WP so there you go...

music player, it's a very big milestone with what they achieved in WP8.1... last time in WP8, I can't stand the music apps... can't even create a playlist without having major headache...