I'm not sure "how to get" a feeling. I'm also not sure of my reaction or how to go about listening if I only just started listening to TOOL.
I purchased 'Undertow' when it was released and it was a hit with me. It was very much removed from the other albums of the time, which if angst was part, stank of marketing. Don't get me wrong, the other albums by Smashing Pumpkins, Nirvana or Pearl Jam (to name a few) were great albums and sincere works by the artists which I love. But TOOL's 'Undertow' had a rare atmosphere. It was much more authentic, personal, psychological, claustrophobic, where there was anger it seemed born of the pain of personal trauma rather than fashion or politics. For me it's very American, very Tennessee Williams. The vocals often have vulnerability which raises the tension.
The whole album is a bit one note-ish in the way a nightmare has a single theme.
When I would come home from a night on the town back then, I nearly always woke on the sofa at 4:00am to 'Undertow' on repeat playing loudly. It just fit with my condition better than anything else (strange endorsement!). I have the fondest feelings about this singularly flavoured album.
Maybe the too well adjusted will never get it?
ænima is much different with a more colourful palette than the two toned, two dimensional Undertow. More extroverted than the introverted Undertow. Expanded musically and with a wider view that is less personal but still very psychological with more personal affirmations. A masterpiece IMHO.
Lateralus was a disappointment for me for quite a while. I thought "Metallica meets Pink Floyd". I'm not into progressive rock partly due to the lack of emotion and Lateralus was much more of an architectural construct than the more soulful Undertow and ænima. But it grew on me as a grandly constructed composition and ended up enjoying it a lot. An intellectual, quirky-quasi-philosophical masterpiece.
Along with Radiohead, I'd put TOOL at the very top, amogst the very few, the royalty, the Crème de la Crème of rock/pop groups active today. The present closest to a Pink Floyd or Led Zeppelin type band with that big sound, big guitar riffs, awesome drumming, integrity, mystery and majesty. Due to a lack of groove and high value of perspective factor, TOOL are more Floyd than Zep.