This is a tough one to comment on.
I think the animation is actually quite good. Its very detailed and while i can't see any real problems with it, i think there are issues with this one which to me are more fundamental than anything (Feel free to argue with me on this people). I couldn't put my finger on it to begin with but the more i think about it the more it comes clear and obvious to me. Anyway, i'll try to be as blunt so to be as clear as possible so if i sound rough, please dont take offense.
I can see two big issues with this one.
1. The character is moving too slow: I can't realy say this because i dont have a context to work with, but my intuition tells me the walking animation is too restrictive. Thats about as quick as he's going to go. Its a 10 frame detailed animation. I'd suggest a 3-5 frame animation that will allow some play in the speed the character travels. Take a look at this one for example:
2. Its hard to identify this guy as a mechanic: This is an open comment. How you wish to resolve this is entirely up to you but i think others will also agree. My suggestion would be to throw a hard hat or wrench/toolbox in on this one just to fit the stereotype.
I also think the shading needs a little work but i can't comment on how to go about this one. I find working with smaller pics much harder as there is so little space to work with on details. Its hard to see his face on the grey background without some outline so perhaps that might help.
Either way, I'd suggest you focus on the major 2 issues. Perhaps it'll be easier to provide some feedback after this. (If i can get my hands on a gif editor i'll see if i can help).
Let us know when you have an update.