I think this game is nice! The graphics are good and it was fun to play. I sadly (barely) didn't complete the final level, if it ends after the three artilleries next to each other... :( Trying to keep the bus from harm can be fun when everything works out.
I had some issues with FPS dropping that made it frustrating at times, I think it particularly happens when the bus gets on top of the helicopter. The level selection not working with the mouse despite the rest of the menu being mouse enabled trolled me quite a bit!
Overall, I liked your game, good job!