I think the head and neck are placed too far back. The stomach muscles are still over-defined too - they aren't consistent with the smoother, undefined musculature of the rest of the body. More generally, all the proportions are off. Not terribly so, but enough to "feel" odd. If I were you, I'd study some anatomical reference images and scale the various parts of your model accordingly.
It's a good start though!
It's a good start though!