I bet you different people worked on CD Denjin <(totally unsubstantiated thought)
I really love the colors and sprites on the first Denjin, even if I don't have the game myself.
I'm putting the occasional time into KiKi KaiKai and Mr. Heli, two far more "drab" looking games but fun (and frustrating) in their own ways.
KiKi KaiKai I come back to every now and then to see if I can get a little farther - usually, yes. This last time making it to the whip-wielding Buddhist priest. You have to be constantly managing threats from all directions, making this a very stressful game as it wears on. Boss fights especially so given the lack of room to maneuver, your large slowish sprite and enemy attacks.
It's a very tough nut to crack; I hope I can get to the end one of these days.
Mr. Heli remains frustrating. If there is a strategy for that f*cking level 2 boss, aka "the giant sphere that kills you instantly thanks for playing", I'd like to see it. It's such a painfully lame boss and early wall to player progress.