Death metal rarely uses drop tuning, for one. The rhythm is an important factor that doesn't come across well in tabs, "bouncy" is the best word I can think of to describe hardcore riffing (esp. the prevalence of breakdowns). Also death metal tends to be more melodic, relatively speaking, and doesn't rely so much on the percussive function of the guitar. Check out which of these Slipknot's riffing matches up better with:
Code:
Cannibal Corpse, "Hammer Smashed Face"
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I--------------------2--------I------------------------------I
I-2h5p2--1h4p1--4-4--0--------I--------------------3---------I
I---------------2-2-----2-1---I--3h6p3-2h5p2--5-5--1---------I
I---------------------------3-I---------------3-3-----3-2-0--I
Hatebreed, "I Will Be Heard"
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-000-0000-000-0000-000-0000-1-4-1-5-4-1
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