Guess it comes down to personal taste. Demon Souls was fun, in the way that megaman 1 is fun: controller smashingly difficult, but worth it when finally overcome the impossible. However, there was no real connection between me, the main character, or the world. It all felt like a semi-lovecraftian high fantasy story being told TO you. A story that would beat the tar out of you with a stick if it even THOUGHT you weren't paying attention.
I don't get the hate oblivion gets. World felt like a wasteland? I got attacked by wolves, imps, weird dryad tree people, bears, and demon crocodiles every friggin' time I strayed from a main road. Every. Damn. Time. In every playthrough. Yeah, the NPC and character faces were sub par, I'll give ya that. And the psychic clone army of town guards were annoying (Nobody was even AROUND when I murdered that one guy, yet suddenly if I set foot into any town anywhere I'm immediately greeted by some dude in full plate screaming "STOP! You violated the law!" or "It's all over, lawbreaker!") The magic system was far from perfect too, mainly in the sense that you had to cast so many spells just to get one level in the associated school of magic. Despite all that I had a blast playing it, and I still do to this day (especially now that I've discovered mods) I can beat this game multiple times and still go back for more playing as a different race and/or a different "class" (I use the term class very loosely). It never fails to be immersive. Every time I play Oblivion I enter an altered mental state where despite the technological limitations and flaws I feel like I am really in a fantasy world. That's what's fun, and that sort of pedigree is what is going to make me put aside my money for skyrim over Dark Souls.