It's pretty bad. Worse than any one I've seen.
Removing the sidebar makes it inconsistent with every other Mac app. Finder, iPhoto, Mail, hell even Safari is based around a sidebar with the content in the main window.
The little icons for Music, Apps, TV Shows etc are inconsistent. If you're in the App Store and you want to see your music you have to click the Music icon. This doesn't take you to your music but to the music section of the iTunes Store. You then have to click back towards the middle of the display on My Music. Troubleshooting this over the phone has proven far more difficult with less "savvy" folks...
Tagging info is a mess.
The top bar is yet again a mish-mash of UI elements.
The Devices icon doesn't reflect the number of connected devices.
App updates don't show the release notes (bug but annoying).
TV episodes no longer have a description without right clicking.
i didnt really like the new itunes update it doesnt fit in with the way lion looks in my opinion considering i cant upgrade any further 