Thanks a lot! Yeah, I agree on there's no 100%. For my day job, there's almost always an edge-case that exists that wasn't anticipated. These are generally found by the users because it's impossible to anticipate for every scenario. So yeah, 80% is a good rule of thumb. The benefit is that you know you'll learn something new from it. So that leaves room for improvement.
I really liked your game as well. Like I said before, the UI blew me away. I was not anticipating the complexity of it and it looked really polished. There were the couple items I mentioned before regarding the UI that could be improved, but overall, I enjoyed it!