I just love how every label comes up with a 'nu' kind of metal, just pick an angsty word, stick it in front of the word 'metal', and Bravo, that's your labels 'sound' 
Doom Metal
Death Metal
Blood Metal
Scar Metal
Burn Metal
Banana Metal...
The possibilities are endless
cept for the first 2 none of those are offshoots ive heard of. while the concept of nu-metal was entirely a corporate ploy to "resurrect" a supposedly "dead" sub-genre of rock, by infusing what they thought was "metal" with elements from the various offshoots of mainstream punk rock. the result was total crap that the kiddies bought up in droves, until they got bored with it and bought into other things, like crappy emo music. record companies dont care how good the music is, so long as its selling.
what they failed to realize that is that metal never died. metal was never especially popular, cept for maybe the glam era and 80s hair metal, which not surprisingly was about the same thing as nu-metal is today (or rather yesterday as it didnt last very long), over-marketed crap. the industry just wanted to stir it up, not necessarily generate any real creativity, just an attempt to milk teenagers of their allowances. real metal on the other hand is something that is not for everyone. it was never meant to be popular, it has never been taken seriously, yet surprisingly has been around for well over 4 decades, and still doesnt get its own rack in most record stores.
anyway metal can be summed up in a few basic sub genres, traditional (aka heavy) metal, power metal, thrash metal, doom metal, death metal, prog metal, black metal and death metal. and of course each of those have their own sub genres (death metal comes in a few varieties, gothenburg being one, black metal has its first and second waves) and there are other crossover genres like goth metal and viking metal. there are many more and if i listed em all would take up too much space. if youre looking for actual "singing" rather than guttural (black, death) or yelling (thrash) lean tward power, prog, or doom and possibly some traditional metal as well. goth metal tends to have
of female vocals, usually soprano, usually paired up with guttural vox (refered to as beauty and the beast vocals). as ford said classic doom metal is usually sung, like black sabbath or candlemass. some black metal offshoots, arcturus for example, have some rather impressive vocals (and everything else too). but anyway if you care more about the lyrics than the instrumentation metal probably isnt for you anyway.
