I would have to say that MAYH and Still Life are the most 'structured' albums that Opeth have produced as a whole, because the theme of the albums runs its course and the songs naturally have to complement that.
BWP, I feel was something more experimental, because they were working with a producer that they were all fans of and took a more experimental approach to the album, and all in all, I really like what they have come up with, I would have to say that it is my favourite Opeth album. He really improved Opeth's production and I guess kind of implemented a new layer to the sound, mainly the airy, stretched out, guitar melodies that have kind of become a trademark to the album. The Drapery Falls I would have to say is my current favourite Opeth song because I totally love the way it's structured, I totally get into where it goes and how it goes about getting there, and the intro and closing sections are there to kind of give the song a trademark sound, almost like a chorus to it. As for themes, I really don't know where this album goes, but after MAYH and Still Life, I really wasn't expecting another themed, significant kind of album. I mean seriously, it was a cool idea and all, and I really get into it but Mikael himself has said that it was irritating to make all the bits and pieces fit in on MAYH and Still Life. I don't mind that it was kind of spontaneous and Mikael wrote about whatever was on his mind, the main theme being death I suppose.
I can really understand why a person would not be able to get into the music and even listen to a song in one sitting, but Opeth is just like that, it takes a certain kind of person to get into it, and I'm totally cool with people that don't, they can just move on and get into whatever interests them.