Welp, I think I'm going to throw my two bits in. Not really ability advice, because I'm sure alot of ppl here can shred me to pieces, but this is what worked for me:
Play what you love, but don't exclude yourself from other styles. I mainly like thrash and speed, but I also like Pink Floyd. Playing other styles will also develop a more well-rounded technique. So when somebody comes up to you and wants to jam, they might not be into the same thing you are....however, if you are familiar with other styles, you'll find that you can learn so much from others and yourself. Now, here are some albums I recommend buying and listening to, mainly for the energy, the ability, and the sound. For me, metal was never about anger; it was about aggression. Metal was never about depression; it was about letting go of your feelings and pouring them out in your music. This is just for ME. Alot of my friends listen to that nu metal crap because it has a kind of mosh pit feel to them. They use it as an outlet. For me, playing and listening to metal gives me a high like I've never felt before in my life. Working on a song for a month and finally being able to pull it off, then teaming up with some friends to play in front of a small crowd of other friends is THE GREATEST FEELING IN THE WORLD. I don't care if I ever get famous or rich or anything; my goal is to be GOOD. If I play podunk little clubs in my hometown for a side job I will, as long as I have that satisfaction of knowing that I can shred anyone I know. That's where I want to be in 10-15 years. Set goals, that is the number one thing. Ok, on to the albums:
THE SPEED METAL ALBUM OF ALL TIME, and arguably THE metal album of all time....Master of Puppets by Metallica. If you only buy the album for the instrumental masterpiece Orion, GET IT!
Rust in Peace by Megadeth is also an amazing album, equal to Master of Puppets in my opinion. Songs like Holy Wars, Hangar 18, Rust in Peace, Take No Prisoners, and Tornado of Souls are classics.
Slayer's Reign in Blood is also a must-buy, if only for the energy. Angel of Death has to be one of the coolest thrash metal songs of all time.
Buy Iron Maiden's Best of the Beast - it has all the great songs on it....make sure it's the double disc, cuz you also get Rime of the Ancient Mariner on it. What a song!
It's not really that metal, but the atmosphere and amazing songs on Alice in Chains' "Dirt" make it a must buy as well. Also, check out Jar of Flies -- that's the acoustic EP.
For doom metal, Anathema and My Dying Bride are the way to go. For Anathema, I recommend the albums The Silent Enigma, Judgement, Alternative 4, and Eternity. For My Dying Bride, I love the albums Like Gods of the Sun, Angel and the Dark River, and The Dreadful Hours.
A band that cannot be classified would solely belong to Opeth. What an amazing band. Get these guys...wow.
For melodic death metal or the Gothenberg scene, I recommend In Flames, At the Gates, Carcass, Soilwork, and Arch Enemy...although Arch Enemy in my opinion doesn't match up with the rest of them as far as songwriting goes...their ability is great and have a great sound.
Straight death metal, bands like Morbid Angel, Cannibal Corpse, Deicide's Legion album, Hypocrisy, Death, Nile, and Zyclon
Now, for the power and true metal....I'm not too well versed, but here is what I have and I dig it. Nevermore, of course Iron Maiden, of course Iced Earth, Control Denied (Death's Chuck Schuldiner's band before he passed away....what a guitarist!)
Other bands you should definitely check out, if only for their amazing work: Agents of Oblivion, Dream Theater, and Therion.
That's all I can think of right now. If you have a DSL or cable connection, go to Kazaa or Morpheus and start downloading to see what you like. That's what it takes to determine what niche you are in. I like everything, but I can't listen to it all the time. Sometimes I have to be in a certain mood for some things...like the harder death metal/grindcore. It took me about two years of sampling, buying, looking, listening, asking and just trying to see where my musical tastes lie. I went from not listening to death and black metal at all to listening to everything in the span of 9 months. I just had to get exposed to it, and that's what I recommend for you to do...expose yourself to everything you can, if you don't like it, then that can be a good thing. At least you aren't short changing yourself and know what you're missing out on. I hate to think about something that I would love that I am missing out on because I just haven't tried listening to it.