Opeth are a Prog Death Metal band. The singer mixes growling and cleaning vocals. The music is very dark and kinda hypnotic, then get's very heavy and thrash. They have 6 albums to date. I like them, but I can understand why alot of people are turned off by them. Their stuff isn't for everyone. You can find Mp3s of their stuff easily on the 'net. Have a listen for yourself.