To all the other misery mentioned, I add that the "Refresh Podcast" feature became nonfunctional, neither for individual podcasts or the "refresh all" button that was (inexplicably) moved from the LRC to URC of the Podcasts window.
But that's not what I'm here to talk about. I wanted to provide a solution, at least for those who still have 11.2 in Time Machine. The problem is that following the normal instructions to restore an item will fail; you'll get an error saying that "iTunes cannot be moved or deleted because it is required for OSX". And indeed, you cannot move or delete iTunes manually; you can't drag it to the Trash and if you try to drag it to the Desktop the system will instead create a shortcut.
But through the magic of the Terminal window, this issue can be overcome, as follows:
0. You have to have root enabled on your machine. You can google the instructions for that, they're not hard. (But it goes without saying that if they scare you, or if using the command line in general scares you, this solution is not for you.)
1. Open a Finder window to your Applications folder, then open Terminal. Type at the command prompt:
sudo mv[space]
2. Now click on iTunes and drop it in the Terminal window. This action adds the path to the end of your typing - it's an easy way of avoiding typos. Finish typing:
sudo mv /Applications/iTunes.app /.
3. Press Enter. You'll be prompted for your user password. iTunes will be moved to the root of your hard drive. We're putting it there in case things go pear-shaped, you can easily back out of the change.
4. Now enter Time Machine and find an earlier version of iTunes. Note that it has to be 11.x; going back to 10 will break all kinds of things. Click Restore. You'll be prompted to enter your password to write into the Applications folder.
5. That should do it. Launch iTunes and make sure everything is still working. If so, you can Trash the copy of 11.3 now in the root of your HD.