Electronic music similar in style/atmosphere to Opeth

to be honest.. I wouldn't say Boards Of Canada are at all like opeth..

But i advise you to download Akira Yamaoka's Silent hill 2 and 3 original soundtracks. You'll no doubt love them.

Also, download Venetian Snare's album "Rossz Csillag Alatt Született". Intense stuff.
I love Rossz, quality stuff.
 
Indeed.. It probably is his best album tbh. It's just.. I can't fault it really. I haven't got a single qualm with that album. But that said, i've not got any qualms with most of Venetian Snares.
 
check out the Norwegian fellow named "Eivind Aarset"....absolutely top-notch electronic jazz-influenced music..

Lots of thick, juicy progressions and dark vibes.. I'd start with his albums "Electronique Noir" and "Light Extracts"