Looks like the normals are being averaged around the corners, which I'm guessing is not what you want. You can get "even" shading on the flat surfaces by selecting the faces along one strip (e.g. the entire line of 5 quads that you've pointed at) and then going to Edit Polygons > Normals > Average Normals. Repeat that for each strip of faces. That should get you clean, even shading on those surfaces.