Just a heads up, you are actually talking about aesthetics here and not graphics, and this is controlled by your artists and not the engine. The actual style and look is the aesthetic principle and really has nothing to do with the engine at all.
I need some engine with really good looking natural graphics. Google screens from L2, I don't like graphics which Tera-Online or AION has.
Also is there a reason you're avoiding the proven solutions like HeroCloud and BigWorld?