I think Maynard showed the most evolution on that record. I'd really like to discuss this also with people and see what others think. TLDR While it's no argument that Lateralus is Tool's most impressive work yet, it all falls back to the sound and ideas present on Ænima. But it only exists because of what was done before, what was learned before on Ænima. It's thunder and lighting and raw aggression, while also being gracefully layered into an awesome show of the greatest sounds heard in metal. Danny Carrey, Adam, and Justin all show remarkable talent. The lyrics deal with getting over things, being a man, showing compassion etc. Maynard's voice has finally come into it's own with graceful touches of melancholy and of course the barks and roars from start to finish. It kicks more ass almost immediately and stands as a testament to Tool's ability as songwriters. After the supposed metamorphosis after the album ends, I like to think that Lateralus picks up after what was learned from the change. In the end it's like all the pain they've endured so far was totally worth it, but not before they stood face to face with the worst of it all. Tool completely embrace taking bold moves to reach a mindset stronger and greater than it was before (on Undertow) and it shows in the albums grand finale Third Eye. Every single song on this record is oozing with Tool's equally dreary and mesmerizing sound. Adam's psychedelic riffs Justin's doomy bass mixed with Danny's thunderous drumming propel this into prog rock perfection. The entire band displays it's unique emotion with such balance.
Focusing on change in the lyrics rather than drowning in negative thoughts and actions. Not only did it expand upon everything that was good in Undertow but the entire album is more of an experience in itself also. While Lateralus is the quintessential Tool album and the perfect starting point for new listeners, Ænima set the bar and would become the main influence for everything they would go on to release afterward.