The plates on the spider monster's back look kind of flat—you need a lot more shading if you want to give the illusion of a rounded body. The shading you do have does not consistently suggest a light source: the head looks like it's lit from the top, the torso and the legs on the spider's right (our left) look like they're lit from the left, and the legs on the other side look like they're lit from the right.
Your human sprite also needs more shading. He especially needs highlights on his hair and face, but he could use some more shadows too, and his light source isn't 100% consistent either (face lit from forward-left(?), left arm—our right—possibly lit from the right). Also, I think there may be some sort of perspective fail going on with his breastplate—it looks like one side is slanted toward the center at the top and the other is straight up and down.
