I think it looks fine, but if you want to improve it that badly, I would suggest adding more depth to the cracks, because from what I can from the image, only one shade of grey has been used for them.
[edit] looking back at it, some of the cracks also seem very thick, so maybe make them thinner. Another thing to consider is maybe also add some bits where it looks like the brick has been chipped away.
I hope this helps you
