I don't mind some of their stuff, but I never really got into them. I wouldn't call them metal though - they are more or less like a more modern progressive rock, I'd say.
One thing that annoys me are many diehard Tool fans. Knowing that I'm into metal, they are always telling me that Tool has one of the greatest drummers, and their vocalist who's looked upon as some sort of a god, can 'scream' better than any metal vocalist. Or how their music is without a doubt the 'trippiest' thing out there, and lots of silly arguments....
However, nothing fails to irritate me more than are some Tool fans who've clearly devoted too much of their life to hard drugs, who think every second of music this band has ever recorded is in someway linked to some mass conspiracy.
I remember hearing about a fan being heavily convinced their Laterus album was meant to be a soundtrack to Mel Gibson's movie, The Passion of the Christ. Need I say more.