Did a quick test with Sonic Lost World: http://youtu.be/SeVp5sY-t4w
Feature seems to be working pretty well here on Chrome, shame the videos don't even load in HD at all in Firefox though.
I thought I couldn't tell the difference because all the comparison gifs in the past looked pretty much the same to me but I just watched a Mario Kart 8 video (sorry if it's already posted https://www.youtube.com/watch?v=_zPm3SSj6W8) and it was so much different, the way everything was moving.