Great game, all levels are challenging in their own way though you sometimes have to spend more than 3 minutes on realizing random little thing that allows you to past the level. I don't think it's a bad think as there is a big satisfaction with finding it out but for some other players it might be annoying. Not killing your enemies is interesting feature that increases difficulty but doesn't make it impossible to pass. I would most likely play an extended version of it where for e.g. you can use both lines or swap between them or have some new types of the lines. I hope you'll continue on creating games like this as their simple to play but challenging to pass.