Dark Souls would be even better with harder settings. More aggressive and relentless enemies, less blockable attacks, more damage done to you, that sort of stuff. I would love it. You take what you've learned, and hone the skills even further as the game in a sense closed it's jaws around you the more you ramped the difficulty up, pushing it's punishment for your mistakes up higher and higher, while pitting you against increasingly worse odds and scenarios.