Thank you for playing the game!
It's in my TODO list to add more levels. In fact previous versions (e.g. 0.15) had more and different kind of levels (sequential circuits and streams) but I had to remove them from this version because they didn't seem to function correctly with the new logic simulator.
Now that I've added the HDL I will certainly add more levels with only HDL components to make the player familiar with it.
In the meantime you can experiment with the sandbox if you want :)