A few things:
1. Where's this Composer view? I don't see it.
2. This update seems to have fixed the resizing problem in Windows, where maximizing the window would cause it to extend beyond the screen. That's a relief, as that was becoming a bit of an annoyance.
3. I'm still disappointed that Apple removed the button that brings you to what's currently playing on the list. Prior to iTunes 11, one click would scroll the list to where you currently are. Now, there's an extra step involved, where you have to click the arrow beside the song title, and then click the option in the list. It's less convenient.
4. I'm still not a fan of how album art is displayed. I usually use the 'Songs' view, so it's disappointing seeing the album art relegated to a tiny little square at the top of the screen.
iTunes 11 is clearly an improvement over iTunes 10 in many ways (speed, performance, creating playlists, cleaner interface etc...) but it also removed some functionality that I really liked.