We've had threads talking about metal for those who like it, but scooting around the forums I notice lots of prejudices and misconceptions about metal popping up, and as I, really, love metal only slightly less than my own left testicle, I thought I'd disabuse some stuff, make some suggestions etc. etc.
There are several points I'd like to make:
1: "Metal is all screaming/growling etc." = As someone who has a reasonably wide musical palette, and wider experience, I have to say that, next to electronica, metal is probably one of the most diverse genres...well, ever. Within the scope of what is generally agreed to be 'real metal' (very little of which you will ever hear played on the radio, btw) are an insane variety of bands, sounds and genres. Metal encompasses a vast range of sounds, both homegrown and exterior: metal bands have been influenced by and incorporated literally everything: space rock, punk, opera, folk music, techno... if you want to get some basic idea at what you're dealing with, get a track from Sigh's latest album and a track from Nattefrost's latest album. That's just the diversity in what you could very loosely call 'black metal'. (elitists debate genre boundaries constantly)
2: I've noticed lots of indie people seem to like Mastodon, Isis and sometimes Opeth. Whilst not meaning to be uncharitable, I think this is mainly because they are the only metal bands you've been exposed to that fall anywhere near your musical environment. Those of you who like these sorts of bands could do with exploring the genre more and picking out other prog-influenced bands: Ayreon )or anything else with Arjen Lucassen in it), Dream Theatre, Wuthering Heights, Amorphis, maybe even the later works of Edge of Sanity/Dan Swano. Then there's the instrument-driven genre of Melodic Death Metal, which will totally throw out any conceptions you may have about the word 'Death Metal'. In Flames, Dark Tranquillity, Eternal Tears of Sorrow, Soilwork, maybe Arch Enemy... be prepared for rawriness here, but all in a good cause. the Older works of a lot of these bands are normally the best, the genre is tired and oversaturated nowadays, but to a new-comer this can be pretty vibrant stuff. Just drop your pre-conceptions. Focus on the instrumentation. A lot of this stuff kills the conception that metal is all about killing people or being depressed. Concept albums about the information age, songs about astrology, punk-like sociopolitical rebellion songs, commercialism, even (som) love: this is what you'll find in MDM, and even more in prog metal (along with the songs about killing people and being depressed of course, but nothing's perfect). Want stuff that's totally off the wall? Try the Opera metal of one of the later Therion albums, or get the wits scared out of you by the raucous Polka metal of Finntroll or Korpiklaani. It's a whole musical universe you haven't been to before.
3: Linking on to the previous point, not all metal is violent, or stupid. Commercial 'metal' (which is nine times out of ten not actually metal) often appeals to the lowest common denominator of it's teenage audience with lyrics about angst, violence, etc. Whilst a relatively common theme in metal, such things are normally treated with a great deal more intelligence and musical ability outside the mainstream. Added to them are all manner of other themes: Fantasy and Sci-fi are a relatively strong one, with some bands turning whole albums into sci-fi/fantasy novels set to music. Metal groups have poltical agendas that cross the entire spectrum, from socialism to the ostracized fringe of neo-nazi black metal bands. Bands have written songs about everything from gun control (Edge of Sanity - Enter Chaos) to nuclear weapons testing (Skyclad - Bombjour!). There are joke metal bands: The black metal band Sportlov sing entirely about evil winter sports (grim snowball wars, the dreaded figure-skaters of Satan, etc.), Satans Penguin's dedicate tracks to themes such as the ultimate victory of Gargamel over the Smurfs. Viking and folk metal have plenty of good drinking songs, as well as rousing battle hymns. Religion and spirituality are a common topic (both for and against), and complex philosophy is regularly delved into by bands such as Borknagar and ...And Oceans. There are all sorts of literary references (Lovecraft and Poe featuring quite heavily as one might expect), concept albums, and so forth floating around.
Anyway, I could rant on for ages...but what I'd like to say finally is, give metal a chance! You may not like all, or even most of it, but there's bound to be at least one or two bands you'll like lurking out there in the vast ocean of metal. If you really like unique, interesting and challenging music that does something different, and are willing to push the envelope of your musical comfort zone, the only thing to do is to get heavy*
* and no, not all metal is even heavy, really.
