I uploaded new version. I tried to get rid of all flaws that you all mentioned. There's "how to play" section now, and there is also contextual help available during the game. I hope that you will all like updated version :)
Thank you for comments. I didn't notice bug with CTRL before, it will be fixed.
There are only one key and mouse needed to play, I don't know what can be confusing about that - but maybe it's because I know that game too well. I think that making tutorial from first mission will be good idea.
Thank you all for comments.
@MoratGurgeh - do you mean that using clay.io achievements api is intrusive? I don't know what's wrong with that, maybe I should replace their default branded graphics.
@RandaxKull - You are right about sound and I will definatelly add it, but regarding to other tower defense mechanics - I don't plan to add anything more to game. It was planned to be simple. In other case, there is always big risk to drown in neverending project, especially if you do it all yourself.
I'll try to make an update soon and get rid of most obvious bugs. Do you people think that it needs some better tutorial/introduction? What else do you think I should improve?
 "Pulse"){kind=icon}
 "Scrap Lite"){kind=icon}