Right now you can use either. I showed to someone and they said mouse would be easier, so now you can choose. As for sounds, I had them, but greenfoot isn't too fond of fifty gunshots noises at the same time. :( It caused tons of lag and eventually an error message.

Yeah, the enemies use that system to shoot, but I think semi-auto for the player is fair. I didn't want people just holding down a key at all times and it firing every 50 counts. However, I may add other weapons in the future that do that. Currently, I am trying to balance running enemies over and shooting them. Do you think it would be better if I went back to just space bar? You couldn't really shoot as fast then, as you would have to use your thumb, or take your other hand off the mouse. Thanks for the feedback!

Also, you should setPaintOrder(scoreboard.class); or whatever your scoreboard is so you can place towers under the board and still see the scoreboard.

Cool, but It would be nice to see stats when you hover over a button to buy a tower. Also, while placing a tower, you should see a circle showing their range.