I was about 16 back in 2001 when I first heard Opeth and it blew me away. I had been listening to some metal, not much though - early In Flames and mid-era Metallica for the most part. I was clueless about real metal and didn't really like death metal screams, although I enjoyed the music. Then I heard "Benighted" and was intrigued. But I quickly forgot about it.
Then all of a sudden a friend sent me mp3s of "April Ethereal", "The Drapery Falls" and "Demon Of The Fall". On listening to them I felt as if I was experiencing something incredible. I immediately went and bought My Arms Your Hearse, and listened to it repeatedly, sometimes twice a day, often in the dark while lying on my bed and letting every note sink in.
Eventually I bought Blackwater Park, Morningrise, Still Life and Orchid. And of course every other Opeth album as it came out. I loved them all and still do, although none of them gave me the impact that MAYH does. This year I'm seeing them for the third time; they are easily my favourite band and have been now for eight years. A friend at work has the "O" tattooed across the side of his throat and my first thought was "why didn't I think of that?!?" My leather jacket has an Opeth back patch, and it's my most prized possession.
They opened my eyes to real metal and since then I have found first a tolerance and then a strong appreciation for much, much more music both heavier and softer - but I can't say it was either melodic music or death metal that made me love Opeth, it was just the exhilerating emotion in the music of "April Ethereal" that still moves me incredibly today. It's the only time I can actually say music has completely made my jaw drop.
These days I listen mainly to black metal or doom metal, and on the softer side of things prog and post-rock, but Opeth will always stand above it all.