I've ridden a KX500 once - one afternoon's worth of incredible, adrenaline pumping joy. It was twenty years ago and I am still not over it. The engine is explosive, with terrific bottom-end torque, and a top-end rush that leaves you with a lofting front tyre in third gear at half throttle.
I'm not quite sure what you are asking here though - not easy to ride? People "almost" didnt like it? The KX500 is powerful, but isn't a corner-carver like the lightweight machines of today. It's terrific on the ice, from what I hear, and for desert racing, and for open courses with straights. I think a pristine 2004 KX500 would make an excellent investment as a collector's bike. It represents the pinnacle of two-stroke dirtbike engine technology, in my opinion. If people "dont" like it, it's probably because their chosen race course is tight & twisty, or that the engine forces them to learn throttle control. You cannot simply "whack" the throttle open on a KX500 without something big happening.