Ha, ha... that may have been the same impression I had when I first debuted his music back in the day.

Watermelon in Easter Hay is one of his best. Zoot Allures is OK. Why Does It Hurt When I Pee is a classic.
But my personal favorite is Dirty Love. Its a more funk rock/P-funk kinda' song though. Not prog.

I think he was just genius in the studio. His album recording's and production is outstanding in my opinion.

Well I've been listening to them a lot lately and I was aware of them since a few years ago; but since the early release of Heroes I've really fell in love with the band. Here's my top 5 Sabaton songs I've gone over it a lot and deliberated I made a playlist.

Ruina Imperii
Metal Crüe
Back in Control
Wolfpack
Masters of the World

Metal Similar to Slipknot
 

Im just getting into metal and I kinda liked Slipknot. I like the polysyllabic poetic lyrics, but the guitar feels a little simple, I'm not sure quite what I'm looking for but I would like some recommendations. Thank you!

Last FM is one of the easier ways to find closely related music online.
Slipknot

Scroll down to the similar artists list on the right side and you're on your way.

You might want to check out Joey Jordisons band Scar the Martyr.

how about mushroomhead?

Five Finger Death Punch, close enough similarities for that to be a valid recommendations as well.

Slayer's God Hates Us All album is a bit Slipknot-ish.

Rather bands that sound like Slipknot, here's some other stuff I think you should be able to dig:

Helloween = Slipknot