Getting planets to look good in realtime is very hard and takes alot of tweaking, in the normal map shader I used for my game I had to specify a Specular Map texture, this texture was basically a cube map for the lighting to use, and if you raised things like the ambient brightness of it then the reflection would dim, and vice vera. So while fiddling around with this eventually you can get a nice subtle shading effects and not some very sharp specular like you mentioned.
Also about the planets rings, I find that use a ghosted object to be the best, as it's easy to setup(creation wise) and looks nice with the alpha blending, I noticed in your screenshot your ring is just a textured plain, I would highly recommend you use a cylinder cap, so you end up with a nice hoop from which you can texture with a cross section of the rings, with around 200 sides you can get a very round looking ring and the best bit is that the texture size it uses is a mere fraction of using one texture and it looks alot better, one thing about ghosting is that you must have the background as black, and from your screenshot it seems you have a white background, you can either invert the texture and ghost it, or save it as a .png or .dds or .tga? with an alpha channel, assuming you either got it with one or made it with one, if not then making the background bacl is the easier option.
