For me it was the music. I started out with the drums and guitar listening to Grunge, Rock and Punk. When I started listening to maiden, tallica, sonata, kreator, my tastes changed.
Metal is like a whole new portal by itself, true freedom of choice, expression and art. Unlike any other genre, it comes with the technical, the funny, the weird, the strange, the melodic, the agressive, the bored, the stoned, the angry..and there are musicians who write songs dealing with interesting concepts of the world, as well as those happy-go-lucky dealing with love and what not. Its basically all-in-one.
In my view, Metal is to the music world as Open-source is to the IT world.
Some say metal is serious, well to an extent yes. There are funny metal like korpiklaani, but its all in the name of joy and not chicks and dough like most MTV bands. It is seriously for the ears and the people. What sets Metal apart from other music and culture is the diverse audience and themes. There are hooligans, gangsters, doctors, scientists, mafiosos, mothers, models, lawyers who claim to be "true Metalheads". Metal can bring chaos like underground Hardcore and Punk, but it can also bring upon a good classic time like expensive Jazz and Classical concerts sometimes targetting blue-blooded ladies and gentlemen. There is also MTV Metal and that adds to the unique field of the genre as a whole, though some bands clearly do not add any significant credit (they do not sound like we need them).
Now the thing about these so-called Poser bands such as in Nu Metal and Metalcore, it's actually just about "ruining the picture". You see, when things such as music labelling start, music is defined wrongly. You have Linkin Park claiming to be Nu Metal just by fusing simple heavy guitar riffs with the turntable. Sure it's a great innovation but there wasn't a need to call that Metal. Now why do I say that? Because if one really wants to label, then label correctly and listen to a wide range of fans and what they think your music sounds like.
Then you have Metalcore. Few bands are really good, but I'd rather call them simply Death Metal because they are mostly that and less core. Others, well, I think they should've stuck to Hardcore Punk. Sum 41 has got Metal sounds, but they don't claim to be an entire Metal band of any sort. Already Dave Baksh has left/is leaving the band to pursue a "Metal career". I think labelling is good, but not when it gets out of hand. It seems almost every culture wants a part in Metal just for the sake of it, whether you sound Metal or not. Then again the definition of "Heavy Metal" can be different from one person to another.
Then there is the culture. Wait, I see geeks and side-zippers. So that means, all the culture needs is appreciation and headbanging, or just sitting and nodding. Long hair, leather jackets, eyeliner, pentagrams, some wear it to be part of the culture and others because they know what they're wearing and for what purpose. There are the elistists and Black Metal supremacists, but I don't blame them because they know what they live for. The Metalcore/Emocore kids took on the eyeliner, studded belts, black colour to be a fashion sense and absolutely monopolised the teenage world. So much so, that it is almost a uniform and a monotonous youth. How diverse and interesting can Metal appear then if a so-called self-proclaimed sub-genre attracts more attention-seeking teenagers than music-appreciative ones?
Themes in Metal can range from Mutilation and Death to Hunting and Food to Dancing and Fantasy. Where else do you find such variety? Let's not get into the technicality of those technical metal bands. As Metal itself takes roots from Blues, Jazz and Classical, many prominent musicians are skilled in almost a variety of instruments. Many of us have idolised one of them at some point of our lives. There are very talented people in the Metal scene, as well as very well-educated and established too.
I personally love some Metal music for their ability to blend melody & aggression, thoughts, anger, happiness & sadness altogether. I listen to all kinds of Metal, except for those I deem unsuitable for my ears. I do not see Metal as a window to self-expression, I see it as self-indulgence. I do not hate any kind of music, I just have my tastes like everyone else. I also love Techno, Electronic, Trance, Folk, Classical, Country. However, I find all those in Metal too! I listen to Pop, yes. When a tune sounds nice, it's music afterall. Let me add something about Metalcore again, LOL: well gore/growl and a sudden breakdown to some clean boyband-like singing just doesn't sound really nice. Not all recipes end up as delicious treats.
), the rise of second-gen. Black Metal and the even more radical ideals espoused therein and really find that style of music and much of the ideology most appealing to this day. I probably listen to BM, Blackened Thrash and Death Metal most of all(though I still love the classic stuff as well) and yes, I do tend to seek out that with which I have some ideological agreement, though that is not a prerequisite. 
