I design board games and I think one of the most under utilized skills is studying other games. (There is old advice that says if you want to be a writer, then read more books.) Go back through all the games you like and write up what you love about them. Then, and more importantly, think a lot about HOW the game makes you feel that way or HOW the game gives you the opportunity to explore in some directed way. Then take that lens and re-evaluate the game that you made.

Every board/card game I design starts with a single key idea or mechanic or theme; but they all have a single cornerstone. Every playtest and design change is always looked at through that lens. If there isn't alignment, then you have two choices: ignore the change or considering resetting your cornerstone given what you know now. This really helps to stop thrashing and give focus to your game as you iterate.