Wow, that's a lovely little design! I'm only in the first few levels so far, but I like it a lot. There's a couple of things that I think let it down at the moment. The interface is awkward, as I think there's a few too many things to click on. For example, I don't like the way you have to select objects from the toolbox and it doesn't seem to tell you what they are until you place them. Because this is what you need to do all the time, why don't you just draw the objects menu on the side of the screen and select them directly from there? It would also be nice if it was clearer what the objects were before you placed them. I'm seeing barriers so far but I assume there'll be more objects to place, judging by the help screen?
Also, I think all that information on the help screen could appear in little hint boxes which appear on the levels where you need to learn them. At the moment there's too much stuff there, but not when you actually need to learn from it.
A lovely design and I can't wait to see it expand!