How to revert to iTunes 11 if you don't like iTunes 12

Some reviewers think iTunes 12 is "Apple's worst software ever" because of the visually incoherent way it presents information on your media collection - in particular, the complete lack of the sidebar, where media were listed by category.

I agree - but luckily, if you have accepted the iTunes 12 "upgrade" you can fairly easily go back to iTunes 11. Here are very clear instructions, from MacWorld repeated on the LifeHacker blog.

First off, download copies of AppZapper and Pacifist , backup your computer, then create an installer with Pacifist. (Pacifist allows you to unpack .dmg installation packages and extract individual files and folders. Not something one needs to do every day! but in this case it's just the job.)

1. Quit iTunes 12 and launch AppZapper
2. Open AppZapper's preferences and uncheck"Keep Apple Applications Safe"
3. Drag the iTunes 12 icon from the Application folder to AppZapper and click the "Zap!" button
4. Download iTunes 11 - from the Apple support site
5. Open up Pacifist and drag the iTunes 11 DMG file into it. 
6. Select "Contents of Install iTunes" and then click "Install"
7. Navigate to your iTunes folder. Within that find the iTunes library and then find the iTunes LIbrary.itl file. Drag it to your desktop or to the trash.
8. Launch iTunes 11.

Done.
- Actually, not quite! Where is my iTunes music and media? Apple support gives the following instructions for retrieving it:

Re-creating the iTunes Library file

Note: After re-creating your library, any devices that you sync with iTunes (Apple TV, iPod, iPhone, iPad) will see your iTunes library as a new library and will completely resync. The next sync with such a device will take longer and may reset some options since your rebuilt library isn't familiar to the device.

1. Quit iTunes.
2. Locate your iTunes folder (this is the folder that contains the iTunes Library and iTunes Library.xml files).

Operating System	Default location of iTunes Folder
Mac OS X	/Users/[your username]/Music
Microsoft Windows XP	\Documents and Settings\[your username]\My Documents\My Music\
Microsoft Windows Vista	\Users\[your username]\Music\
Microsoft Windows 7	\Users\[your username]\My Music\

3. Open your iTunes folder.
4. Drag the "iTunes Library.xml" or "iTunes Music Library.xml" file to the Desktop. If neither is available, learn how to add files back to the Library (because the XML file is not available, playlists and other information will not be available).
5. Drag the following file from your iTunes folder to the Trash:

Mac OS X	"iTunes Library" or "iTunes Library.itl"
Microsoft Windows	"iTunes Library.itl"

6. Open iTunes.
Important: Do not add any content into iTunes at this point (such as by purchasing something from the iTunes Store).
7. Choose File > Library > Import Playlist.
8. Navigate to the "iTunes Library.xml" file on the Desktop.

• Mac users: Click Choose.
• Windows users: Click Open.

If your Podcasts list in iTunes is empty after following these steps, learn how to add them back into iTunes.

Hooray, it's all back.

Doubtless Apple will try to "upgrade" you to iTunes 12 with every software update. Click Details instead of automatically accepting and you'll be able to avoid the horrid thing.