I am happy you enjoyed the game.
In terms of time spent playtesting. I spent a lot of time with an initial test room getting things to work in kind of a sandbox environment. When I finally started building out levels and playtesting them, ideas came out from that process that I just kind of followed. However, I think I started that playtesting and level building phase a little too late and that kind of led to a lack of polish in some areas. One of those being what you mentioned with a lack feed back on some of the clear containers and when actions failed.