Upbeat has nothing to do with lyrics, it has to do with the music, Slipknot don't sound nihilistic, the shining sound nihilistic, Slipknot sound like a lot of rock bands out there only much heavier. Upbeat is also not just a feeling, it's part of the beat in music when you conduct and is used heavily in dance as well.
Back on the case of lyrics, I can think of plenty of Nick Cave or Johnny Cash songs which are very depressing and have nothing to do with metal what so ever.
"You are one of gods mistakes you lying tragic waste of skin" is one of Placebo's lyrics and that is on par with anything slipknot have written.
I gave my opinion as to what I believe the genre of metal entails.
Originally Posted by MisterMixelpix
Oh yeah. "I push my fingers into my eyes, it's the only thing that can stop the ache". Very upbeat. C'mon man, Slipknot is one of the most nihilistic bands that has ever hit the mainstream. Look at the entirety of "All Hope is Gone".
And whoa now. Grindcore is a very different beast from hardcore. It's intentionally atonal, fast and chaotic, usually with song structure thrown out the window. There's so much more to it than simply "faster hardcore". The difference between a Pig Destroyer and a Hatebreed run FAR beyond tempo. They're totally different styles of music.
"Metal" is a huge umbrella. HUGE. Most metalheads don't even agree on what's good and what's not. You run from power metal like Dragonforce to grindcore like PxDx, death metal like Brain Drill and black metal like Emperor, prog bands like Opeth and Dream Theater all the way to drone bands like Sunn O))). "Metal" as a genre itself doesn't exist, really. It's too wide.