Think I know what he means and I'd agree, though its not my favourite opeth album.
Complete because it has an intro that sets the tone for the album, the songs flow well into eachother (much like blackwater park) and the songs themselves flow well. Epilogue is just a classic finish that would look great on any rock album, but really winds down a death metal album very well.
Its not really palpable, completeness, just a feeling you get, you don't want more or want it to end soon, it just feels right.