The first reaction that I got is the wrong use of blue (ultramarine). I did not realize it when I started with it, but when I did, it was too late.
Prabal helped me lift off some colour. But, I wanted to keep it that way to remind me of the mistake. Also the red bricks seem too saturated.
As again, I have a smaller version which I sketched and painted in 10 minutes..and looks better than the bigger one :)