If you want a real challenge, though, it's worth playing the classically infuriating Battletoads, a game that the vast majority of players have never even finished (myself included). The infamous Turbo Tunnel is the hardest level in the entire game, one which has probably broken more controllers than just about any other I can think of, but there's also a tremendous feeling of accomplishment once you get past it. What this level does is ask the player to do something that they don't have to very often anymore, and that's remember things. The key to getting through the Turbo Tunnel, given the sheer speed at which things move, is memorising the various patterns in which enemies are thrown at you. It took so long to memorise, but the feeling of making your way past it was immensely satisfying, and it ended up being one level you could absolutely beast on a fairly regular basis once you'd gotten past it just one time.