I'd second either Stil Life, or My Arms Your Hearse- these two are Opeths classics, the only albums that have truly come together. Blackwater park has some excellent riffs and many fine moments- but it meanders on and on with really no point. The last two albums Damnation and Deliverance were definately a big step backwards- Damnation isnt as good as the acoustic songs on any of their metal albums- Deliverance has an added heaviness- but that is it. Notice how no one is recommending those two albums either. I think the Opeth fans have come to terms with how mediocre the last two albums were.