Honestly, this game probably doesn't belong on the list any more than Defenders of Dynatron City, but I lobbied hard for this one in the voting process because there are elements of it, and particular levels, that make this game extraordinarily difficult. I am thinking most specifically about some of the absolutely vicious feats of jumping the game asks you to perform, be it skipping across a lake like a stone or rebounding off trampolines across a bottomless chasm. The are parts of this game that ask you to be so ridiculously precise that it is not unfathomable that only the most skilled, dedicated, or stupid have ever seen the end of this game. (does that double negative really work there, I mean "it is fathomable that only..." just seemed more awkward...)
For the record, I have beaten Kid Kool all of twice. Once a few years ago, and once last year for this project. The most recent accomplishment was done in four and half hours of nearly non-stop playing. I say nearly because anyone who has played this game knows that you have to take occasional rage breaks (a common feature in this list) to prevent from destroying more financially significant aspects of your environment. I would probably play Kid Kool a lot more except for one glaring problem, the game gets frustrating early and often.
And I am not even kidding. Once you hit level three, all bets are off. The game throws absolutely unfair combinations of enemies, jumps, and obstacles at you in rapid succession. The control mechanics are not your friend either. In order to make long jumps you must get a running start, yet there are many places where there simply isn't a lot of room to build up speed. The game screen is technically two screens high, but if you jump up or fall down a screen, then game stops, scrolls the screen, then resumes the action. This causes a lot of problems establishing a fluidity of motion in the executing the precise maneuvers they want you to perform.
The end result is mounting frustration and a desperate need of your endless continues. You need the continues because you may be doing several levels or parts of levels many, many times to get past them, and once past them you'll not turn your NES off until the game has been beaten because you never, ever want to have to do that again. The frustration will come when you finally breach a certain area that you have been trying to get right for the past half hour, only to die immediately in the next tough section and have to do both again.
All of the above being said, the game can be beaten and the unlimited continues mean you have plenty of time to get it right. Part of the game play is a countdown timer that represents how much time the King has before he succumbs to his malady, but that timer is an idle threat. You have more than enough game time to take the game out, no matter how many times you have to make a run at a certain level. Kid Kool makes this list because of its insidious level design and high level of frustration. Many people will get fed up before they beat this game, making it hard enough to be in the Top 30 (29 really).