@Boltgreywing Getting play testers the next step once you think you have something solid. And of course have something to test. Honestly it is all just so subjective, as there are many styles of play and games as well as different people. So that is why I recommended playing it to see if it feels fun. Getting play testers is great too though.
Then ask good questions to them. Is the game fun? What do you enjoy about the game? What frustrates you about the game? Etc... Then you will have to analyze yourself to decide where to go. That is the part that makes you the game designer, and not just the programmer. It's not easy. But if you are struggling with that step, I'd recommend playing games and analyze why you like them, What do you like about them, don't like about them etc..
I do that all the time still. It's part of what being a game designer is about.