The textures are ok, but the lighting is super flat. People are used to games making at least some attempt at global illumination, whether it's prebaked light maps, or faking it with SSAO, or anything to not have surfaces be a totally consistent brightness across the whole thing.
Your rendering API is not going to implement GI for you, and having it in a sample app is kind of misleading, that's not really the point. It's probably a mistake to include that as a sample scene as it creates the impression that it's trying to be a game engine. A few material spheres and test meshes would probably be a better example.
