First things first... it's huge! You could scale it down to a third of it's current size and it wouldn't hurt it. Would also make it more manage-able to work with, and closer to be called pixel art.

Anyway, from what I've seen from your other thread, this isn't on par with your current level of skill. Right? Why not re-do the sketch and work from there instead? That would make our critique more accurate. But I'll post what I'd originally thought to write anyway.

His stance is awkward, it looks like he's falling forward. The coat movement suggest that he just started to move, backwards. These two things conflict and make the image difficult to read.
You need to work on your facial anatomy. The eyes looks like he's a madman (if this is intentional that's fine though), but the face need some fixing up. Check pictures of real people in that pose. The body is okay, but could need some work, mostly in posing. Although... he has six fingers on his right hand! 

The way he holds the guitar looks very uncomfortable, especially if he's moving about. I would change it so that the guitar at least face the other way, otherwise the strings would get stuck in his hair when he moved. It would also make it easier to work with without losing the effect the guitar was intended for, since the silhouette of the guitar would be more important than the details.

Finally I'd say, take a few steps away from manga/anime and learn to draw actual human beings first. I had to do that myself. It's worth it. When you get the hang of anatomy there's no trouble in doing manga style again.