Since I've got the bulk of the engine complete, I'm currently designing all the levels. I've got some general ideas and principles I've been following and it seems to be going nicely. I'm actually quite surprised how well everything is coming together.  I've written my own level editor that has allowed me to streamline the level creation. I think development for this one will be complete within the next month or two. The way I've designed this one, I'll be able to continuously add new maps even after the game's release. Right now, I've got three and a half levels complete but I still have more to go!