Good basis, needs serious work
Guitar is great. The design and the pose are okay. There are serious problems, though: the hands are way too big. They are also really gnarly looking compared to how smooth everything else is. His hat looks like it was cut from a bucket, and you'd be better off with a textured half-sphere. The eyes shouldn't be so round, more like squat ovals than circles. The nose you can keep. He should have some expression in the mouth, and it should be less wide. The chin is also a mixed bag: either make it protrude a bit in the Z direction (out of the page) or round it out more in the X and Y directions so it looks more cartoonish.
The biggest general issue is that you keep going back and forth between a cartoony look and a realistic look. Character modeling isn't easy, and I think it was overly optimistic to try it here when the guitar looks so realistic.