I'm a rather new fan, as I have only Heritage, Watershed and Blackwater Park. I'm one of those folks who listened when people said "if you're not sure about the harsh vocals, get Heritage to see if you like them for their songwriting, then try to get into the growly ones." Of those three, Heritage is probably my least favorite while BWP is my favorite.
But, I wanted to contribute this as someone who heard Heritage first: The album sounds, from a compositional standpoint, like their earlier albums. It sounds like someone turned down the distortion on the guitars and Mikael decided to stop growling, and also Slither just got on there somehow, but for the most part, it sounds like the Opeth approach to songwriting, just applied to a new form of arrangement, and sometimes not even that. The first time I heard The Leper Affinity, when the acoustic section began, I thought, "this sounds just like something off of Heritage!" I know it might be weird to read it that way as I'm sure most people heard TLA long before hearing Heritage, and I'm not demanding that people love Heritage (especially since, as I would agree, it is a huge change of direction), but all I would suggest is to give Heritage a listen and then listen to The Leper Affinity and some other of the older songs and see if they can't hear the similarities in songwriting style and in arrangement for the folky parts, and applied to a different arragement for the heavy parts.