I liked the grunge episode, but I have to agree that it didn't really explain a lot, and the last segment seemed to be more of a glorified promo for Nickelback than anything else (which is where my interest started waning, because I absolutely cannot STAND that band). I think it was meant more to explore the question of "Okay, what was it about this genre that completely killed metal in the 90s?" and it kind of bombed in that respect.
I expect the nu-metal episode tomorrow to be filled with many, many cringe-worthy moments and bands I hate. Apart from Rage Against the Machine, that was a scene I never got into. Rage, at least, had substance. Not to mention one ridiculously creative guitarist.
Death metal was never really my thing. I've always been more of a thrash, classic, and prog kinda metalhead, myself. I could count on one hand the amount of death metal bands I actually can claim to like, although one of them I'd put more in the prog genre (Opeth), and I'm not quite sure where some of the more melodically focused bands like Dark Tranquillity and Arch Enemy fall on the death metal ladder. But the interviews with Corpsegrinder and Alex Webster in Headbanger's Journey were pretty cool, so I'll definitely be checking that episode out when it airs. The one I'm looking the most forward to is the prog episode, as I said earlier, because when I started getting into that, after spending the majority of my youth flying the flag of Priest, Maiden, and Metallica, hearing Dream Theater, Porcupine Tree, Fates Warning, and Opeth was kind of my "What the fuck have I been missing?!" moment, and working back from there into Rush, King Crimson, Pink Floyd, Frank Zappa, and the like.