IMO,
as opeth moves away from the heavy end of heavy, moodwise and often musically, employing a greater number of colours in their palette, i find it interesting that two musicians whose styles i feel are very "metal" have joined. i can appreciate watershed, though it isn't really my deal, it's an interesting vibe being created with these two- blazing trad-metal solos as on Heir Apparent, and the metal-ish, mechanical fills on that enormous build-up section of porcelain heart. i hope it all comes together for me as a listener on the next album.
it is certainly a different sound, i wondered listening to the record how it would sound with the previous lineup. as time goes by and they play together more, i am sure a new unified unit will emerge on the next record, which i am confident will top both of the last discs, while being nothing like either. fresh blood! don't like the changes? listen to the older records they aren't going anywhere!!