These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV tropes about the band itself:
Award Snub: The 2003 Grammy awards nominated both Slipknot and Stone Sour in the Best Metal Performance category for "My Plague" and "Get Inside" respectively, giving Taylor and Root a 2/5 chance of taking home an award. Korn won that night (Slipknot won three years later for "Before I Forget" while Stone Sour is one of the most nominated bands without a win in the category's history).
Broken Base: ...over the shift away from their nu-metal beginnings.
Jordison's departure from the band and Grey's death also broke the fanbase quite a bit. Jordison and Grey wrote a good chunk of the band's best material and some are worried that the rest of the band won't be able to match up to their song writing.
With Jordison out, Taylor, Root, and Crahan fit this role now.
Fandom Rivalry: Mostly with Mushroomhead fans. Juggalos and Maggots are also rivals somewhat, even though Slipknot's members are Juggalos. Insane Clown Posse and Slipknot are actually mutual admirers, although ICP is not fond of Slipknot's decision to call their fans "maggots".
The hidden track "Porn and Weed" on Slipknot, in which the band is recording themselves watching a scat porn video, including at least one member throwing up. This may also Cross the Line Twice for some, especially due to some of the comments the guys make.
The band released a box set that included a DVD in honor of the 10th anniversary of the release of their first album on September 9, 2009, or 9/9/09 (a reference to the collective name "the nine"). The very first scene on the DVD, following a foreword by Crahan, is of Wilson vomiting for about a minute and a half.
Nightmare Fuel: The song "Iowa" is basically nightmares given auditory form. Other creepy songs by them include "The Virus of Life", "Tattered and Torn", "Prosthetics", "Scissors", "Gently", and "Purity."