Spike introduced me to My Arms, Your Hearse about 2 years ago.
I liked what I heard even though the vocals took some time getting used to. I was(and still am), a fan of bands such as Iron Maiden, who have clear vocals.
My alll time favourite Opeth songs would have to be:
Epilogue from My arms, Your hearse,
The Apostle in Triumph from Orchid.
All of Opeths songs are great, but these stand out the most for me.