As others have said, you're not really letting the puck roll from heel to toe which doesn't give it much stability. With a ball, all you really need to do is just start pushing the ball and angle your stick and it ramps off of your stick no problem.
First thing I'd work on is just controlling the puck well enough so you can chop it back to your heel. Try to cup the puck on the heel, and make sure you do it well. If you seat the puck against the blade well, then you'll be able to get the proper snap on it.
Wrist snapping is the other part, first you cup the puck, open the blade a bit to start it rolling down the blade, and as you release close the blade and roll your wrists so it rockets off of the toe and has a nice spin to it. This guy demonstrates it really well:
http://www.youtube.com/watch?v=GCwFOR9P6Dg
Last bit I'd suggest is working on the release part where you use your top hand to pull back on the stick. I find that using balls, you tend to use your lower hand a lot more to guide the ball. If you do this with a puck, you don't get the proper acceleration to ensure that it stays stuck to your blade and you get a poor release.
To me, those are the three most important things you have to focus on in order to get a good release. Everything else on top is just for power and accuracy.