My main issue is the user interface. It could really use a lot of work, due to the extraction/injection stuff and events like newspaz mentioned. It was also very cumbersome only being able to select and place one tile at a time.

Being able to select multiple tiles at a time like in JCS might be a bit too complicated, but a feature where you could place multiple tiles at a time would probably be easier to implement. By this I mean you could do something like click and drag, creating a solid box of whatever tile you have selected. This would make it so much easier to place ground, walls, and so on.