I'd love to give other gamers the same feelings that I experience when I play games. With the game I'm currently making (co-op 2d shooter) I want people to have the same fun I did when playing co-op games with friends and family when I was growing up. In the future, I'd like to do some tugging on emotional strings as well using things that inspire me and hopefully others too.
It's also a pretty fun hobby of course. There's not a lot of things more rewarding than watching people play and enjoy something you've created.