This is very nice, a great attempt at Zen. The monotone color scheme and soft sense of lighting makes it work and keeps things minimal. Great job from the 'Great Job Baggie'!
I bet if the pepple was off-centered in this image you would score .3 to .5 higher. Personally, I like shallow DOF shots and this one is good for the challenge. Good luck.
This is just me, but if you were going to use a dead center placement, I think you would have been better off using a square format. For me, if you were going to use a rectangular format, you should use the rile of thirds and have the pebble off-center. Very zen feeling in the tones and use of depth of field.