What happened to over half of my music with this new update?

I Just installed the latest updat on iPod 64 gig. Now over half of my music has disappered. I am be becoming very frustrated with all of these changes to the music. I have payed a lot of money for CDs and also to itunes. It feels like you are ripping us off! I had been thinking about getting the new iPhone, but am feeling like it would be a wast of time!