Touch control sounds like a good suggestion that would make the game more accessible. I'll look into it!
I've thought about revealing the source code, but the main problem is that you'd need to own Game Maker and deal with my spaghetti code. So I'd rather do a sequel with a proper level editor instead (featuring a user-friendly interface, and support for easily sharing levels). But I'm not really sure if & when that will happen, my other projects have priority at the moment. Sorry!