You could sink thousands of dollars into art, into board design and franchises and it might help your game be better. Might. You could hire experienced game developers, or sell it to a reputable publisher and hope that they might improve it. Again, might. You could think and analyze and build spreadsheets, balance odds and payouts and it might let you see how well your game will play.
But if you want to know, and know in the easiest possible fashion, then there’s only one sure fire way: watch your iterations.
An iteration is a cycle of prototype-playtest-improve-new prototype. Wash-rinse-repeat. Over and over and over again. The number of iterations is the one thing that a designer has total control over, the one thing that will improve the game, will make it reach its full potential.
For every iteration your game will develop. Occasionally an iteration will take your game in the wrong direction, but that’s improvement too: knowing when something doesn’t work, when you’ve got to cut off a branch of your design and let it grow down a different path.
Once your game starts to approach its final stages, the point at which it, or you, can’t go any further, you’ll see the amount of changes between iterations lessen. You’ll be down to polishing the final touches. And you’ll reach the point where your iterations either stay static (i.e. you test one version over and over) or start bouncing (you change the game, realize it’s become worse and revert to an earlier version).
At this time your game might or might not be good. It might or might sell. It might or might not be improved by outside assistance (almost always it might). It might or might not be better if you put it on the shelf and try redesigning it in a year or two. But, right now, it will be the best game you’re capable of making. And you’ll know that.