I do somehow never played G.R.U.N.T.S myself, but reading 3run's review I do somehow get Blattsalat's points.
Released games, especially paid games, need to be bug free(The 'fun', 'well balanced', etc is obvious). That's where beta testers play the part. You can't beta test your game your self since you already know your game, what are the "do and don't" in your game. Instead ask your family or friends to play the game and watch them playing without saying any instruction(Will be better if you ask a real beta tester though). If you like, give a prize for those finding bugs in your game

From 100% of game development time, 90% would/should be spent on polishing and beta testing.