I love Death Note! It's my favorite anime! Let me explain some things in it that you seem to have misunderstood.
First off, Light's name. In the original version of the manga, his name was not Light, but Ratio. I don't know why newer versions of it have his name as Light. I guess it was so it would be easier to have an English word instead of a Japanese name for the American fans. His last name, Yagami, is Japanese. The people who made it are Japanese. Spelling it backwards to spell out "I'm a gay" in English would mean nothing to the author.
Second, the Sinigami, or gods of death. The author meant for them to be a real creature, not to be taken seriously by viewers. In fact, when the characters in the book found out about it, they couldn't believe it. By now, your child should be old enought to tell the difference between fiction and nonfiction.
Third, you said the main character, Light, was in love with the detective, L. I honestly laughed when I read that because so many people think that they were gay. The scene you were talking about with them drying each other off wasn't anywhere in the manga. They added that in the anime for no good reason. Also, if they're gay, then why did Light kill L and why does Light have a girlfriend?
Fourth, the notebook of death. Light uses the Death Note to kill criminals. He thinks it is right, but obviously, it's not. I think the anime makes that part clear when the police all over the world are looking for him.
Fifth, Light saying he is God. Light is mentaly insane and needs to be locked up in a padded cell with a nice little straight jacket. Enough said.
Finally, the music. I loved the music for the anime. It really created a feel of suspence. I don't think it's bad at all. There aren't even in any words in it.
I think you should let your child watch this as long as he knows it's all real. Just be glad he's not watching yaoi (gay anime) or yuri (lesbian anime). And remember, in Death Note, just like most other tv shows, the good guys always win
