I posted this in my own thread "still having problems with MC 13" but since your concerns were basically the same as mine, I thought I would copy and past my solution in your thread too. I had not gotton to the editing yet and how it differs from MC 12 but I was not able to double click on a song anymore in the main library details screen without being forced to go into a stacked view of the album cover and artist song list. The music would not continue to play while I was in the main library detail screen either; selecting shuffle did nothing. I was also having problems with it showing incorrect album covers for the artist I was listening to.
What I had to do is create a playlist, [I called it Shuffle all] copy and paste my entire library in it, and in that playlist, the music will continue to play music after the origonal song was selected. I can also double click on a song without having to go to that stacked split screen view with a view of the album cover. To make MC 13 act like MC 12, I have to basically stay in that playlist I created with my entire music library in it.
... the Album art does not match the artist. I was able to get rid of the album art by high-lighting my entire music library and right clicking, selecting remove cover art and allowing them to be removed from the HDD.
Now all I see is a musical note next to the song details or a green play arrow up top. I like that better than seeing the wrong album art for an artist.