unresponsive jump-buttons render this unplayable.
Well, just jumping from a standstill doesn't work very well because of the way the super-condensed jumping system functions, that's why I put the emphasis on bouncing, which lets you just hold the button down. Also, as the game is about 160 screens in size, you'll want to get a good bounce going for speed anyway. You can even gain height by bouncing into clouds, which will give you an added boost.