The sound effects are much quieter than the music, being able to adjust the volumes to a level between 0% and 100% would let the user bring them into balance
The buttons need to provide immediate feedback which way they're selected. Fade in/out looks great, but doesn't create perception of responsiveness. My suggestion: change the color of the button when pressed (grey to dark grey, e.g.), and keep the fade in the animation.
That said the new cum effects are pretty nice (though hard to trigger) and I haven't seen that much attention paid to the butthole animation in quite a while.