Fluid motion.
What I liked about this movie was the use of motion. The paddles went back and forth and the ball's motion smearing was pretty good. The different ways the paddles confronted each other kept the movie away from monotony. The rain and background were nice touches to the movie, and I think it helped set the tone of the movie.
The choice of audio was good. It wasn't intrusive, but it could still be noticed. It had an eerie feel to it, and without it, the movie would have felt empty.
Unfortunately, it may have been too fast to enjoy comfortably. I would say the paddles should have started off slow, as if it were a more regular game, but quickly escalates to the level of "violence" you show in the movie. The paddles "wiggle" around a lot and stretch and contract frequently, and you could work on making straighter paddles that look and behave as rigid objects, not abstract lines.
Using ping-pong is a good change from generic stickman movies, and I think you should start trying out frame-by-frame animation that goes "beyond" stickmen. Well done.