Bugs in the "upgrades": the one that slows down the ball should NOT be able to be nested. I got that upgrade and it slowed it down, and great, that makes it easier. But then I got another one and that made it INTOLERABLY slow. The one that makes the paddle wider sometimes also PARALYZES the paddle! I couldn't move! If this isn't intentional, fix it. If this is intentional, then get better taste, but it sucks.
Also I'd get rid of the gravity term. I notice a small downward acceleration. Just make the ball go in a straight line, and reflect off of surfaces with the usual angle of incidence=angle of reflection rules. Don't put gravity in it.