(-) 1. The halfway down the ramp was uneven. The so-called frictionless material were simply laid on top of the bumps of the hill - The guy would have fallen out from the ramp even before he reached down half of the slide with that kind of speed.
2. The sound effect is too loud for the almost frictionless material. The sound must be added in post-production.
3. I suspect he is flying higher than the place he slid from, which is not possible in physics.
(+) Very believable CG.