You're colors really arnt good..
, you're pillow shading.. pillow shading = BAD! And you are too consistant with your color location. You must create a light source. Light source meaning choose a place that the direction of light comes from and shade it according to the direction.. Obviously in this case it would be coming from the top, so what you would do is place you're lighter colors towards the top of the image, than your darker colors towards the bottom thus giving a feel of light direction. You're bottom shouldnt be roundly shaded as you're top is, as the bottom should be flat considering that the object is basically a box with a rounded top. But, here's a quick edit on your chest to give you an example of what im trying to get at.
Although this was a very quick and kind of crappy edit (i know it lacks in certain areas).. it should give you a push towards where you should be.