Well Rainard, how important is it really that any group must make leaps and bounds on every single new release? Isn't one of the main draws of Opeth the fact that their sound, even as it changed from
Orchid onwards, was consistently something of beyond-competent quality composition, both technical and lyric-wise? And over a whole decade at that....
Personally, I would say its fairly difficult for ANY group currently around right now to meet your rather pompous expectations when for the most part, Opeth HAVE improved themselves in almost every instance over the course of their 9 studio albums (and yes, even when compared with Ghost Reveries, I do think they have grown a bit on Watershed).
This isn't avant-garde we're talking about here. You can't expect massive growth on every single damn release. Opeth are not the freakin' Residents! Keep your expectations grounded in reality or YOU WILL be disappointed. Its that simple.
Not to mention the fact they kick-ass live no matter what they play...