In contrary to monotone hip-hop, cliche
R&B, or computer generated bubblegum pop or trance music, death metal is played by people with instruments, who have the ability to generate melody from said instrument. In contrary to the similar style Black Metal, the lyrics are rarely a mere worshipping of Satan, but are usually about life and death, religion, and deeper things that people who agree with most of the above comments usually don't think about. There's a big difference between the better and worse death metal bands, and many crossover genres are used for originality in the music. For example, there's viking death metal (Amon Amarth), melodic death metal (Scar Symmetry), thrash death metal (Konkhra), black death metal (Naglfar), orchestral death metal (Hollenthon), and many others. The diversity of death metal is but one example of the many subgenres of metal, which is of course the most advanced kind of music nowadays available. The reason death metal remains underground is due to the facts that people are brainwashed with music that is so easy to swallow that they are unable to comprehend the complexity of more advanced kinds of music such as metal.
Several examples of death metal are mentioned above.