Damn. You HAVE Orchid, MAYH, and BWP but have never even heard Still Life or Morningrise? Strange.
I think the middle three Opeth records are the best (Morningrise, MAYH, Still Life) and the other two (moreso BWP) are a bit of a notch down. If you already love Orchid it's hard not to be blown away by Morningrise... it has the same feel and just turns everything up to 11, more epic, more progressive, more emotive... Still Life sounds probably about what you'd expect the album between MAYH and BWP to sound like, except that on the whole, it's a little more jazzy (drumming with brushes on "Face of Melinda", a jazzy guitar tone to the little midsection to "Moonlapse Vertigo", amongst others), and with more clean vocals, and yes, the most soft sections of any record yet.
Morningrise and Still Life actually seem to be the favoured albums amoungst Opeth fans... we did an "Opeth Song Survivor" which was won by Morningrise's "Black Rose Immortal" over Still Life's "The Moor". They generally are 1-2 in the "favourite album" polls. I don't see how you could POSSIBLY be dissappointed...