This is the obvious one. Her movements all happen at the same speed, one after another, with no real pauses in between. It's like lookleftlookrightturnbodyswinggunshootetc, only in kind of slow motion. It's why the eyes look weird--when people look around, their eyes dart rapidly from one place to another, pause, then dart somewhere again. You have them rolling around her head without stopping. And that's just one example--the human body has a ton of very specific ways of doing things that we can't necessarily remember when we're drawing, but subconsciously we can tell if something looks "wrong."
This is where video reference comes in super handy. You're off to a good start using a webcam to shoot keyframes, but don't stop there--shoot a whole video of you acting it out. Figure out not just what poses the keyframes are in, but where are on the timeline, what frame number are they and how many frames are in between each pair. In my first animation class they made us shoot video reference for EVERYTHING and time it out and even our very first animations came out looking pretty decent as a result.
This is the other thing. When something moves, it doesn't move at a constant speed. It has to fight inertia the whole way. So if I move my arm, it's going to start slow, speed up, then slow down to a stop. It "eases" in and out of the motion. A bouncing ball doesn't go up at a constant speed and then suddenly start going back down at a constant speed, it slows down more and more until it's stopped for a split second, then starts accelerating back down (here is an accidentally but conveniently over-exaggerated ball bounce test I did showing that).
Your animation doesn't really show much easing at all, which is the main reason it looks so stiff. Fortunately it's not too hard to fix, just draw frames of a beginning movement closer together and have them spread out in the middle, then bunch up again at the end.