Quite simply Tool's best work.  After just acquiring 10,000 days, along with many listens, I can still honestly say Aenima is still their greatest album.  Strong in all aspects, lyrics, instrumentals, meaning, organization of songs, etc.  Some people who expected Tool to maintain their Opiate and Undertow sound have been disappointed, however, good bands that survive a long time tend to change their sound and Tool has done that successfully on this album.