Notice that in your image, there are no specular highlights. Final gather does not emit specular highlights, therefore making everything looking flat, like you have here. You must add in lights to create that specularity. If you also have any ambient lights, nuke that as well.

If you need any help, PM me the file, and I'll take a look at it.

Also, with Maxwell, I find it quite easy to use if you go through their tutorials on their site.