Outside of the first two albums, I think Demon of the Fall is the easiest heavy song to play. The chorus part takes a little getting used to, but as a total beginner at the guitar I found that the techniques needed for the chorus were pretty good practice for the harder stuff in other songs. Master's Apprentices is pretty manageable too.
Acoustic: Patterns II, To Rid the Disease, Hours of Wealth, and Benighted are all quite manageable for even inexperienced players like me. Fingerpicking is a must though.
The solos that I've found to be easy as a beginner are Windowpane, To Rid the Disease, Wreath (the first one, though there are a couple of arpeggios), and Master's Apprentices (the first one).
I don't know if everyone will agree with this, but I think Opeth is actually a pretty good starter band in terms of aspiring metal guitarists.