Believe me, I understand completely. Demon's/Dark Souls are my two favorite games -- ever -- for all the reasons you listed.
They roughly doubled the amount of hidden lore; I had a great time puzzling it out, as I'm sure you will.
Atmospherically, Dark Souls presents the opposite side of the coin shown in Demon' Souls, and does it really well. In DeS, you enter an area and immediately think, "Something bad happened here." In DaS, you feel instead that something good had been permanently lost. It's similar in some regards, very different in others.
(Have some ranged attacks handy for BP Selen Vinland, by the way.)