Interesting Alex

I think I'd like to add another dimension to your thinking and include GMs.. without whom there would be no games to have a payoff 

As a player I think the payoff for me is designing and creating  a character who has a specific personality recognisably different from those I've played before and with specific goals in mind. I think it's best to have short, medium and long term goals. The goals tend to be mundane in many ways (being able to talk to people without tripping over your tongue, getting married and having children, understanding different cultures, being able to forge end-user certificates for captured javelins, being more interested in the spirit world and neglecting physical things or possessions). I don't think I've set out with a character to gain power, wealth or fame. Some of my characters would die of embarrassment if they were recognised as a hero.

The idea of 'superhero' characters that always wins is a bit redundant for me (well since I stopped playing D&D 30 years ago). I think for me it's actually roleplaying a character true to their personality and goals that brings the satisfaction, even if it is counter to 'winning'. Being able to navigate the scene or scenario brings payoff and solving or at least trying to achieve a solution is positive too. 

As a GM the payoff is designing and running a good session. That it engages the players, makes them consider choices and consequences, poses problems that have moral and 'real-life' consequences and the solutions do not necessarily benefit them. I also like to confuse them by presenting a seemingly simple event that has many layers that they may never understand because that is how things actually work. Leaving them uncertain and unsure gets them thinking and engaged.

So as A GM the payoff for me is definitely engagement at an intellectual level that makes them think about what they are doing, wonder what is going on and create discussion and thought in between sessions where the players are trying to solve whatever situation they find themselves in.

The payoff for me is that it is an immersive experience where there is actual engagement in roleplaying rather than mere process or playing similar characters. If I can engender thought, mystery, confusion, fear, wonder... then I think I have succeeded