Just my opinion on 10074 test preview, but most of the modern apps are so buggy you can do very little with them. For example I had to open Firefox to make this post as spartan just kept refreshing every time I tried to make this post.

Music app is quirky to say the least, sometimes coming up with cant find this song or cant access it. Yet all my music is in the cloud and a copy on hard disk with the music app pointing to the folder.

Insider hub wont log in just sits at the opening screen then says check your internet connection.

Outlook seems to work ok but doesnt pick up all your account from one preview to another which saves a lot of setting up as the previous mail app did.

Those are just the apps I tested and at least feedback now works as with other builds it was intermittent.

MS say that Windows 10 is nearly ready for release, I hope not as there is a lot of re-coding to be done with just the few bugs I have found. No wonder Windows 8 still has bugs!