I find myself unable to stop listening to Opeth's Still Life and My Arms, Your Hearse, and other more melodic stuff like Haken's Visions. Could you guys recommend me some progressive metal concept albums with stunning riffs, melodies and storylines which I can dig into? Cheers.

If it helps with recommending or if someone else likes albums like this, here are some other concept albums I'm really digging at the moment:
Sleep at the Edge of the Earth by Wilderun
Quiet World by Native Construct
Pelagial by The Ocean
The Never Ending Way of OrWarrior by Orphaned Land (actually, pretty much anything by Orphaned Land except for All Is One)
(Most of the stuff by [Luca Turilli's] Rhapsody [of Fire], yeah I know it isn't prog but I find that many of their songs have at least a somewhat proggy feel to them)