^ That album (#31) is rated way too low. WAY too fucking low.
(Just kidding. I realize you have probably only listened to it a few times.)
P.S. - I would classify it as psychedelic instrumental post-doom.
P.P.S. - The other album is more trippy and cerebral, but still quite heavy in parts. If you liked Opus Alter, you'll definitely want to check out Opus Primum as well.
EDIT: Pretty decent assessment of Ensiferum as well. I felt the same way.