Honestly, there's not much to say. The clip is only a total of four, maybe five frames? I'm sorry, but I find it hard to believe that this took long enough on your part to justify any in-depth critique. That said, I will try my best to get you headed in the right direction so you don't mistakenly post something so insubstantial again.

What frame-rate are you working at? It appears to be less than 12fps, so I guess the first thing I would suggest is to bring that up to twelve if it isn't already there. Anything lower tends to look more like a slideshow than an animation. Past that, the stills you took are so far removed from each other that you can clearly differentiate between individual images- even for fast actions, the figure's movement between each frame needs to be much smaller if the animation is going to look convincing. Attempt the test a few times using different increments and observe the results. If you can't get stuff to stay still long enough to take certain frames, try using blu-tak to secure everything.

I guess my final comment would be that, given his substantial momentum, he really should go all the way through the door. As it stands in the Youtube video, he just stops on top of it, which smacks a bit of laziness. Of course, it's possible that Youtube might have cut off the end of the clip; in the future, you'll probably want to leave a second or so of empty space at the end of your film so people can see the whole thing, especially when it's this short.