I love the co-op elements, they're so original and rewarding. I will get back into Demon's Souls once I finally get into Dark Souls and I think I'm gonna purchase it when I get into Uni this September, if I'm not too busy with first year work this would be amazing to tide me over the weeks haha. I remember when Dark Souls was announced, I was so excited.
With Demon's Souls, what I loved most about the worlds was after you defeated a boss, you conquered that level. You were victorious and it made me feel so good that I had achieved that after spending hours upon hours on trying to beat the levels haha. The thing is, the game never felt repetitive and it kind of felt like an action MMO offline. I loved seeing ghosts of other players it made me feel like I wasn't alone in my journey. :L The blue ghost / red ghost element was very well done, and I expect this to be the same in Dark Souls? I haven't researched it much as to avoid spoilers but I seriously can't wait to claim the game.