I really like your use of colors on here. They're really nice to look at. You might want to work a little more on your light and shade, though; the guy would be twice as cute if he were round. You've got the right idea--on the cave walls and pipe. Maybe www.rebekahlynn.com might help with some shading ideas? And don't forget to shade with complimentary colors (not black!)

Keep up the good work!