Ditto to what's been said already. Just curious - did you use tracing paper or a lightbox when you did your sketches, or did you just draw the frames up side by side? The reason I'm asking is that it's very difficult to get a fluid-looking animation by doing the latter.
For the sake of being thorough, I'll go into some depth here. There are a few problems that jump out immediately: One is that his walk is not symmetrical at all. When a human being walks, under normal circumstances, his right and left appendages legs are moving just as much, just as far. This rule is broken when a person is staggering, drunk, limping, etc. In your animation, his right arm is moving much more than his left arm is. If you did this in real life you would lose your balance and fall over, or veer off course.
Problem number 2 is that his feet aren't moving smoothly. When your character is walking in the game it will be presumably at a constant speed. The background will be scrolling by at a constant speed. In order for the animation to be convincing, the foot that is currently resting on the ground needs to be passing underneath him at the same constant speed as the background of the game, because that foot should look like it's staying in one place while the rest of his body passes over it at a constant speed.
Maybe you already knew that and just have to refine the animation some more. Either way you're going to be better off doing your animations either directly on the computer, or investing in a lightbox or (if you're broke like me) some tracing paper so your hand-drawn animations can be more refined.