I am an Opeth fan and I live for Death Metal! Opeth isn't really a Death Metal band though, if anything they're more of a Black Metal band. But overall, they're in their own class
Opeth really got me into Death and Black metal. At first when I bought "Black Water Park" I hated the growl singing. A few days later I thought it wasn't too bad, then I thought it sounded kinda cool, then I liked to just listen to it a lot. Now, I practically live to sing the death growling! I don't know why, I just love it! The frontmen of Skinless, Severe Torture, Napalm Death, etc. are all great death singers.
Children of Bodom is Black Metal.
Yeah, the defining characteristics of metal subgenres are very small and often hard to understand. It takes a lot of reading, talking, and purchasing of metal cds to get a good grasp on the subgenres. Quite rediculus, but I love it! A new book called "The Complete Headbanging History of Metal" is a perfect read to understand the history of heavy metal. But I am know metal expert, so to speak. For example, I still haven't gained a solid grasp of what makes Melodic Death Metal.
Speaking of Melodic Death Metal, everyone check out a new band called The Black Dahlia Murder. Many people call them Melodic Death, but they sound like Black to me. Whatever, just check them out.