Well I'm not very good at explaining things, so I thought I'd do an edit:
First thing I noticed is you had a lot of gradient going on with the shield itself. Then with the gold you outlined it with a very light shade, essentially making it look very pillow-shaded. You also have an extreme lack of highlights that something such as a shield needs to reflect its material. Contrast is also a good thing that this seems to lack. It's very hard to discern the shades of color, making it look very flat and dull.
AA is also very important to two contrasting colors -- this will stop colors like the gold and black from sticking out like a sore thumb against the red.
I wasn't sure of the perspective you were going for, the shape seems to imply a typical 3/4 view, but I may be wrong.