I don't think they are nearly as good. Mario Bros 3 apparently inspired Keen, but Keen was always very slow-paced, because of the one-hit death system. You also

I don't think they are nearly as good. Mario Bros 3 apparently inspired Keen, but Keen was always very slow-paced, because of the one-hit death system. You also needed to defeat enemies with a gun, which was less risky and fun than jumping on the head of enemies like in Mario. Ammo was also limited, which again rewarded slow and careful and boring gameplay. The slower gameplay did fit the few puzzles, but those also weren't too great. I didn't play Keen 6, but I assume it's about the same as 4 and 5.