I recall going through that Nu-Metal phase not too long ago. Before that, I was a huge fan of mainstream stuff. For a while, I remember being obsessed with KoRn, Disturbed, Static-X, Coal Chamber, and a song or two from Slipknot sadly.

Eventually, my music tastes have shifted and I wanted to explore many other types of music. I think the first subgenre of Metal I got into was Gothic Metal. I know it's not the heaviest of metal but it was a start with bands like Tristania, Mandragora Scream, and Paradise. I also got into Power Metal bands like Kamelot, Nightwish, and Symphony X.
Other bands I like are Cannibal Corpse, Bloodbath, Arch Enemy, Darzamat, Septic Flesh, and Therion.

But yeah. I have a diverse taste with metal. I don't consider myself a metalhead because I like Industrial and Rock but I'm always interested on people giving me new recommendations on bands I've never heard of. I'm trying to get more into the Death, Black and Progressive Metal genres. Don't know if you guys consider Progressive Metal "true" metal but I like bands like Opeth.