Pretty much all the graphics are created by the users. More or less everything that you can see.

Other than that, the engine is quite a capable one, but with all content created by users and streamed, it won't ever look as good as a title that has been hand-tuned by professional artists and modelers that are working to maximize the strengths of the graphics engine, and have all their content preloaded on your hard-drive at runtime.

That's just how it is for collaborative environments.