This picture is very cute. I like how the dog is wearing the birthday hat and there is cake in his bowl. It seems to be very well planned out and the picture turned out great.
Photo seems dark to me, not enough lighting on the dog. I would have liked a closer in shot, effectively getting rid of some of the distracting background, and to see more of his/her face in better focus.
I can't believe you got him to keep that hat on. That's too much. Wish the photo had been lighter and brighter. He's a beautiful dog, and deserves to be seen in his best light. Still not a bad photo.