I wish the model was closer in proportions and silhouette to the concept art. I still don't quite understand why CG models always end up so 'safe' instead of sticking to the whacky proportions and daring shapes of the designs. In this case a lot of the appeal of the character is lost in translation - the closeness of the eyes, the endearing ears, the tiny bump of the chin, the oversized hood (which I'm sure would not be fun to rig).
But onto the texturing!
It would be nice to see the flat texture(s), so I can see what's shading and what's shadows cast from the scene. For example - the 'drop shadow' that the front pocket casts on sweater seems rather heavy, but maybe it's a product of the lighting. Just color map, no specular or bump?
I think you could go to a bit more effort to make the sweater look like cloth, and the hair a little more like hair. It's a little distracting that the denim of the jeans has so much detail, but the rest of the texturing is flat by comparison. A nice reference is the cloth in say, Toy Story 3 or Up. Very subtle cloth textures or shader work. It would be nice to see the pinching of the cloth around the wrist in the texture - it helps sell the surface as cloth.
It's a little hard to see, but it looks like the drawcords of the sweater are thinner and black on the model? They really don't read very well, certainly not as well as the original concept art.
When I first laid my eyes on this art - divided into two illustrations -, the first taught that came to my mind was "Hogarth Hughes". The kid in display has a 50's vibe going for him, but the first illustration wants to make sure that he's from our age, by seeing he's wearing a "The Simpsons" shirt under his jacket: he's visual would be nostagic, and not reflecting his era. The second illustration - the 3D rendering - feels much more straight in visually declaring the character to be indeed from the 50's.
The first illustration seems to display the character in a reaction, while the second displays him is a more "universal" pose, as this would be the one illustration that would represent him better, the first appeal. The first illustration doesn't seem focused on "presenting the character" as it seems to be part of a compilation of expressions, and therefore, the first illustration kinda marries with the second.
Last but not least, it's a charming-looking kid, that just for his visuals, seems lively and curious, and not cynical. Of course: I'm judging the impression the art is giving me, using my bias. But what I would say is that visually, the character is compelling and very well made, to the point you would have a "picture" of how he would be in motion, interacting with others in a game or cartoon.