Here's my two cents, and this is my first post on the Opeth forum...
I bought Blackwater Park when I was about 15 years old, I'm 21 now so I've been into Opeth for quite a while. Blackwater Park blew me away with the intricacy of the musicianship, and the atmosphere the music created (good production I feel). All the songs were excellent!
When Deliverance came out, the songs were really well written, but I felt they were a bit more simplistic in terms of composition than the songs on BWP. And also the production on Deliverance didn't have as much atmosphere to it as BWP (it did in some parts but overall I felt it was lacking). In a way I felt the Deliverance production was slightly too clean... I think some of the guitar effects were done in pro-tools etc, this might have been different to the recording techniques for BWP. Damnation came out, and it really was brilliant, the production was spot on and the songs were great.
When Ghost Reveries came out, I did enjoy the experimental side of it, but I felt that like Deliverance, the composition in some songs was simpler than usual for Opeth, and the production felt kind of similar to Deliverance (but with more atmosphere). Baying of the Hounds was an excellent track, but apart from the addition of keys (which sound very effective), I don't think that Opeth had progressed their sound forward (I mean they had definitely shown a more experimental side, but the overall sound of the band wasn't progressing significantly, which isn't necessarily a bad thing anyway).
And along come these two new tracks off Watershed, and all I can think to myself is "YES! This is the stuff!!!!" It feels like this album is the next logical step after BWP. It has the dark atmosphere of BWP, but still has some great evolution to it (Mike's vocals and the keys, and the oboe). It feels like BWP, but with tasteful hints of experimentalism (if thats even a word) thrown in. The composition no longer feels simplified, in fact it's probably more complicated... But the music is very dynamic this time. 10/10.