Painting looks clean enough, it just need something to bring out the details as the Commander says.
Notice how the skin and the shirt is almost blending together? Even his suspenders doesn't really stand out against the shirt.
Play around with some washes, or even some Quickshade. I think it would do a huge difference.
Before trying out Quickshade I'd recommend you doing some additional highlighting, as it will enhance the Quickshade even further.
Good luck!