From most reviews I gathered that a general feeling is that Watershed is a brilliant, amazing album, but doesn't give the same kind of goosebumps people had with previous albums (specifically Blackwater Park and Still Life mostly quoted). This is pretty much according to what I already wrote a couple of times about the development of Opeth and about Watershed ...
Anyway, there is nothing wrong with Watershed ... it is brilliant on its own, and it also provides an interesting perspective on the future, which nobody can predict I guess. They surprised everyone with every album, but every time people were able to formulate ideas about what is to come (even though they were often wrong, hence the surprise every time), but I think now it is pretty much totally unpredictable what is to come next.
But I must say, brilliant as Watershed is, and even though I play it several times daily, it is lacking a certain amount of catchiness that other albums had (maybe this is related to my above statement). Not per se a bad thing, just very different ... reasons for it might be the higher degree of complexity that Opeth is aiming for, but also less emphasis on melodic aspects of the music (read the interviews before the album came out about the influence of Scott Walker).
Just some random thoughts ...