ive only play demons souls, not dark souls yet, but ive played ninja gaiden and ive been led to believe that dark souls is similar to the first. that said, ninja gaiden is great, but can be insanely cheap in its difficultly. demons souls was very well designed, fun, and challenging without being cheap. ninja gaidens harder (but only on the harder difficulties) so if ya want the biggest challenge, get ninja gaiden 2 and try it on master ninja. if you want to have more fun, get dark souls.