Well, about a year ago few guys in IRC we're praising Opeth, so I asked one of them to send one song to me. Well, that song was Demon Of The Fall.
Before that, the heaviest band I listened, was Dragonforce. I had tried to get into Emperor, but it was just one big chaotic soundwall for me, and I couldn't listen to it, without getting a headache. After DOTF had been on my playlist for a few months, I started to notice that hey, this sounds good! Well, then I decided to download (I feel bad about this.) Blackwater Park, because I heard it was good.
I liked Blackwater Park, so I downloaded (I feel bad, again.) the rest of the albums. I've been hooked ever since

Nowadays Opeth is one of my favourite bands, right up there with Led Zeppelin, Neil Young etc.
I can listen to Emperor now too
edit: I've bought Orchid, My Arms, Your Hearse and Ghost Reveries. I'd own the other albums too, if I'd find them somewhere ;P