MY OPINION: Joey is a good drummer for Slipknot. However, if he were to fill in for Carter Beauford at a Dave Matthews Band concert...
The point is that he is proficient at what he does, and most importantly, what he likes doing. I'm sure he and his band just have a great time playing their own music around the world... isn't that most of ours' dream?!
Yes, some of his drumming might get repetitive after awhile, but I owe Joey for getting me into metal drumming; you wouldn't think it, but that stuff requires a good degree of chops and speed, which correlates into skills elsewhere, as time goes on. I do count him as an early influence, and I gotta hand it to him for helping me get where I am now. Learning "The Blister Exists" and "Left Behind" note-for-note wasn't easy for someone who had only been playing about two years, but man, did it help me! Looking back, I'm glad I did it, because it prepared me for genuinely harder stuff, like jazz fusion and prog rock... e.g., Dave Weckl Band and Rush, Dreamtheater, etc...
As it stands, I like Joey Jordison and his drumming, not only because he was an influence when I started getting serious with the drums, but because I like some of the stuff he does... "Liberate" anyone?