The only thing that frustrates me going back to demons souls is the crystal lizards not respawning
Well, having a weird set of rules for when they can spawn. It's a pain in the ass. Try to never let them escape
It's kind of better that way.
The thrill/ rush of trying to get a Crystal Lizard is completely lost in later titles once you learn you can just quit/ reload next to their spawn location if you mess it up. At the same time, missing critical upgrade materials in Demon's Souls can be a major loss and very frustrating. That aspect should've been lightened up by making all of them farmable elsewhere.
In other words, I'd rather Crystal Lizards have weird limited spawning rules like DeS, but just don't make it suck SO bad if you miss what they have.