There is a sound effect for getting hit, however it's not as noticeable as I'd like. Adding a flash to the sprites would definitely help a lot.
It is indeed from scratch in java, specifically Processing 3, no engines. After voting is done I'll clean up the source code and put it up.
The smooth look comes from using a low pass filter between the camera and the target(player). like cameraLocation = cameraLocation - smoothing*(playerLocation - cameraLocation ). Also using a velocity vector for the player, with acceleration, instead of just hard left or right.