Isn't there a lot of alternatives to instagram? I know for Nokia users we have access to Creative Studio. For other manufacturers they generally has their own equivalent as well. Then there's also Fhotoroom which is free and I find pretty powerful. I've never used instagram, but from everything I've seen it seems like the appeal is the ease to share and effects you can apply.
Appwise, coming from iOS in an iPod Touch, I'm not really missing any apps, usually there's some alternative. Sure the actual app might be better (for me it's Micromedix and ePocrates, but I can use MPR.specific games is also something). That said there isn't anything to cause me to think, "wow wish Windows Phone had that app," as there's, as I stated, an alternative for just about everything.
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