Opeth's most technical album?

[DE]

Definately "Moving Death".

 

[fadingessence]

i'd say still life too, i've just starting learning the guitar parts to White Cluster, Face of Melinda, and Serenity...bloody hell! I'd kill to be able to come up with a riff like that!

Definitly those middle albums though, Morningrise is pretty straightforward and Deliverance is downright easy. BWP is a little of both, but personally i'd say it is pretty damn technical and VERY layered.