If I were you, I'd start with just 2 key frames. 1st one standing straight like an idle pose, then 2nd one taking a step forward. Keep switching between the two keys and you should naturally be able to see that the head should shift up and down just like any human would. You have most of it nailed already, just there's no "bounce" to the walk.

@JerryPie i tried your suggestion, but it seem to me that vertical motion doesn't fit well to what's happening with the rest of his body.

@Zizka. Yeah, the head is a pendinng part i must fix sooner or later.

I really doesn't see a lack of flow in the legs motion. Maybe the fluidity is broken by a lack of continuity in the shading.or maybe i placed the legs in some awkward position in some frames. I'll see what can i do.

Thank you both sincerely for taking the time to make suggestions. Learning to see is not easy job (at least for me) and this type of comments help me to be more aware of little details.

Animating the head would be nice as the others said. There's something wrong with the leg cycle however, something doesn't flow. The torso part flows well but they legs don't for some reason.

Hey romanticpixels, if you just shift the head up and down a few pixels throughout the animation it will accomplish so much.  It's a very easy trick I've used over the years and requires almost no work.
 
This only took me about 60 seconds (I shifted the head left and right depending on the chest location).. It's a very rough and quick edit.

This is a pretty solid animation overall though, the cloth flowing is awesome. -- My only complaint would be the feet seem to be skipping a bit, and his gait is a bit unnatural.

keep it up!

Yeah, i wanted to add animation to the head, but my attempts didn't go too well. I'm working on more animatios, but definitely his head is something i need to check back later.

Thanks!

Wow, nice detail :D
I think it'll be perfect if the head have some animation as well.
Still awesome though!