Is it a "hyper-casual" game (Easy to play) ? If yes, continue. Does this game, although easy to play, have a mechanic which involves skill? If you ticked both of these boxes, you're on the right track! Keep doing what you're doing. If not, chat GPT can help you brainstorm some ideas! Best of luck.
I believe levy0's reply is precise enough (thanks for the help). So I'll just add: I can see how the general idea of FPS fighting waves of enemies can work if well executed to meet the theme.
