The music app has only made one improvement since Windows 8 was released: play music from Onedrive. Windows Media Player had a lot bigger improvements between Windows 98 and XP.
The Mail app in Windows 10 has gone worse now that Word is used to render HTML emails. It's now just as bad as Outlook: http://imgur.com/a/J1r7S
Edge? It seems there is only 1 team working on that and they focus 100% of their time supporting new web standards. I like that, but what about the interface?
I feel like Microsoft doesn't even bother with the apps. You certainly don't need to upgrade to Windows 10 for the new apps. I'll be staying with Windows 8.1 for the next couple of months until I see some real improvements.