Just about every single Opeth song has amazing riffs, but I'll name a few favorites;
- The Drapery Falls: intro/outro, 4:02-5:03 (the ahh part and the solo, just beautiful), 5:50 (that heavy riff that sounds awkward but awesome), 8:12 (acoustic part).
- The Leper Affinity: 8:00 (before piano), and the amazing piano outro.
- The Moor: 3:27, 4:27 (with that guitar in the background playing gloomy notes), 5:57 (the clean tremolo part and the heavy chorus), 9:03 (clean/acoustic part), 10:19 (that heavy chorus again).
- The Amen Corner: 3:13 (that beautiful acoustic/clean part)
- Karma: 0:59 (with the ohh/ahh part), 3:53 (that clean interlude), 5:24 (both guitars going at it, just sounds moody), 6:34 (that clean part sounds awesome).
- Madrigal (entire song), I wish it was a full song 10 min song, of its own.
- Moonlapse Vertigo: 0:47 (that part sounds kinda depressing but I love it), 5:00 (that jazzy interlude), 7:15 (plus the outro).
- Bleak: 1:20 (break of morning, coldness lingers on!!!!), 5:20 (that jazz interlude), 6:40.
- Face of Melinda: 5:04 (I think this is one of my top fav riffs of all time, it's too depressing and too good to be true), 7:03 (outro, one word=amazing)
- Harvest: 3:03 (the end of the chorus).
- When: 3:01 (that clean part and the heavy part).
- Circle of the Tyrants (opeth version): 4:20 (that clean part, man it's too atmospheric and too great), rest of the song afterwards.
there's so much more, I'll leave it there.