I really tried to enjoy Demon´s Souls....I like the fighting mechanics, the environments, etc...but the lack of checkpoint systems, making me replay the same areas over and over again, made me give up playing.
I heard about a new, bonfire system in Dark Souls that would finally act as checkpoints, but I´ve read comments that it´s not really the case...anyway, I don´t know, I´ll wait to see.