Composition: 4, Mostly centered composition. Could be improved by moving the snail up to the top left .. giving the snail space in which to travel. As is, he's at the end of his journey. Keep in mind the rule of 3rds and use it to your advantage.
Technical: 6, Sharp where it needs to be. Illustrates shallow DOF (good).
Appeal: 5, Just average appeal... I think a better composition would help here. Also, you might try playing around with the contrast and/or saturation.
Challenge: 5, Nice close-up. A more "macro" version would get right in that little guy's face!
Overall Calculated Average Score: 5, Technically okay. Needs to show a little more creativity.