Just get as many people to play your game as possible, and start play testing early. Play test as soon as you have the main mechanics.

Hi Tuskat,

The less unexpected roadblocks there is for the players, the closer the playtime estimate should be.

I've completed the game after about 45 minutes and now that I know what to do, 10-15 minutes is around the time it would take me to complete it again. I think to give better playtime estimates, you have to get better at finding unclear elements of your game(s). For example, there's two important things that could be communicated better: 1) You have to use the environment to kill most of the enemies 2) A button stays activated if anything touches it. Once I understood these two things, the game became a lot clearer/easier.

I know there's some text that hints at the first point so maybe I'm just slow, but I still think it could be better. One reason I think I was confused, is that the first time you encounter an enemy you are required to kill it with your weapon without the environment. Also why would there be a shotgun upgrade if I'm not really supposed to use my gun? Why is there even a gun? It seems like a crazy question, but if the game is focused on using the environment, why not go all in! If I was forced to use the environment, I would have had no room for confusion. Anyway, all I'm saying is the design could be tighter.

About my second point, I think just changing the button's sprite or color when it's pressed could be enough. Generally I find it's better if things change visually according to their state.

Finding the unclarities in your work is definitely a difficult task; I know I always leave some in my games and it's mostly what gets people stuck (that and difficulty spikes). You will get better with experience though. Getting feedback from people is also a big help. I don't know exactly what your friends told you, but maybe you could ask them to be more specific? I find you really don't need many testers to find the most obvious problems.