The UI changed a bit. You have to go through some tweaks to get it to look similar to iTunes 10. Song view is what make is usable for me. The album viewing in my opinion is more obnoxious.
You can even get the Podcast page to look similar.
The music is in the same place that I put it in 2004.
They moved some of the commands around a bit so finding Convert ID3 Tags and make AAC Version is a bit more challenging as they are no longer in the Right Click context menu, they are in the File menu. Creating playlists has moved a bit too.
It's really the same thing, just harder to use. Outside of that it seems pretty much the same thing, organized strangely.
They should really look at their actual user base, not their intended user base for the design decisions. I know no one in my physical life that uses iTunes Music, iTunes Match, iTunes Connect or Genius. So why are they so prevalent in the application? Why do we have to configure our system to hide cloud music so we don't see duplicates? Why can't app updates automatically download?
Yes I support the use of the application, that does not mean I love the application.
Some of their use cases are weird too. Like not being able to sync an iPod while iTunes Match is in use.
Overall it will be a slight learning curve but you'll get used to it. There is not really an option when you want to buy a new device.