I think that by making the transition from the top plane to the sides a little less sudden you'll add volume and make it more believable.
My rough and dirty edit:
I also think your palette can use some work; It's rather monochromatic right now and although that's a valid stylistic choice I personally think you can make it look better by modifying some of your hues.
Overall it's looking good so far, and I prefer the textured cracks version.
