I am by no means a snap change master (heck, I can barely do the snap change), but here's my advice
From videos I've seen I think the snap change looks more impressive when you keep the hand stationary and just flick the card a little bit. That way it's more surprisng to the audience. In other words, I think there was too much motion used.
Then again, what do I know, I'm just a pass freak
