How to mass-organize iTunes library?
The free (and open-source) program MusicBrainz Picard would be a good option to consider. It can identify songs and albums by their acoustic ID's and automatically enter the ID3 tags. 

The program will "play nice" with iTunes as well. Just use it to organize and tag your music, then do the following (copied from the MusicBrainz Picard website)


Open iTunes, then go to File > Add Folder to Library
Point it at the top of your iTunes directory ("My Music\iTunes\iTunes Music\Music" on Windows, by default).
iTunes will rescan your music.