One possibility might be, that the normal map was created based on the diffuse texture. I think the tools and plug ins, that create normal maps from 2D textures use the brightness values of the image. Often darker parts of the texture are lower, but in this case the spaces between the bricks are very bright, almost as bright as the bricks. So I would recommend - before creating the normal map - to make a greyscale copy of the texture and manually darken the parts between the bricks, to make sure, that the normal map has some depth (like a bumpmap).
I would also use the alpha channel to control the specularity. Bricks are usually not very shiny ...