Hmm...It seems alright, but I agree, there could still be quite a bit of work to do on it. I suggest coming up with a flowing motion with your hands/wrists after you seperate the deck into 4 packets at the start - For example rotating your wrists until they're crossed. All the parts of the flourish some kind of disconnected, there needs to be a kind of continuation of motion there. Such as about half a second before the actual drawbridge move, I see an opportunity to move the cards in a wave-like fashion, a bit like a vertical snake. That would solve the slight awkwardness in bringing the packet in your left hand up and then immediately down again.
Finally, it feels like there needs to be something more at the end as a closer - maybe a quick revolution cut with your right hand just before you toss the packet into your left?
It's definitely pretty cool though, and I like the song and video editing.