First off, welcome to pixelation! Second...prepare for blunt feedback!!
I'm not really sure how to even crit this. The eyes look painted on, and they look like they're looking upward, don't know why they would be though. The mouth looks off center. I don't have any idea what those indents are about either. Why is the specular along the front edge just as bright as the specular along the top edges? Why is one eye AA'd while the other is left jagged? Why does the thing have a big black outline around every form? Why are the mid and mid-dark browns so close together?
Finally, why are you drawing, um, Boxman? I mean I'm all for sketches and practice and learning new things, definitely, but something like Boxman here doesn't necessarily give us a lot to go on as far as advice. It kinda looks like you started following an isometric tutorial and got bored halfway through. If you really wanna help Boxman, take Joseph's advice to heart - focus on the 'man' more than the 'box' and start building some interesting shapes and silhouettes!