Nice art style and I like the slingshot mechanic.
I just wish you had gamepad support. I've had a real hard time to time both right click and left click right while jumping. But that might just be me. I am not good with Keyboard and Mouse. :)
What would really add a lot to this game would be some eerie background music.
Also, I am always very impressed by people not using engines, but doing it the old school way, like you did with C++. Congratulations to you!