I think gameplay is one of the most important factors, i wouldn’t play a game without it. But what is it? I believe it is the structure of how the game handles and how rewarding it feels to play. I would say it was made up of several factors, the way you input commands, the way they are performed, How challenging vs how fluid both are, and how rewarding the overall outcome is. That is what i believe gameplay is and that is why i believe it is a definable set of rules no matter how you go about creating the game and hard ware, if you play it with your hands or whole body, if the game gives you a million unlocks and a zillion points for a kill, none of this would be fun if it wasn’t for my stated factors.
So how should they work? If you are playing the game, you want it to be easy to tell it what to do, the input needs to be fluid and not complex but hard enough to be challenging, example a button combo of five would be acceptable for an amazingly rare finisher but if you required that every time it would be boring and repetitive, same with if it was only one button to execute every skill and move. The way they are performed should be instantaneous and responsive; the A.I. should be smart enough to know if such a command was necessary, like approaching a cliff edge where the character hesitates instead of walking blind to his death. Finally the game should be rewarding to play, replayability is a good feature of gameplay, going back to the start for a reason makes you want to play it again, and having a more challenging setting makes you feel you’ve worked for such a setting. This is what makes a good game, and with that, I believe gameplay is important and exists.