Here are a handful of apps that I use both on my Lumia 1520 and my Galaxy S5. I've tried to list a few areas where the Windows phone variant falls down.
|Amazon & Google Music|
I could go on and on but you get the picture. Yes, there are many apps that do not exist in the Windows phone marketplace but even the apps that are there are generally quite bad when compared to their Android or IOS counterpart. I'm a Windows phone fan and want it to succeed but there is an app gap and don't let anyone tell you there isn't.