Unity's actual power is belied by the poor quality of the default shaders (especially shadows) and weak assets commonly used in amateur games. A dedicated graphics programmer, backed up by professional-quality assets, can get a lot of mileage out of it.
This, this and this. For top notch presentation, you need good art, first and foremost. Then the graphics substrate needs to pack enough punch. The engine is the canvas and the brush and the paints - but not the painter. Art is not a random linear combination of default assets no matter how many cycles you use for your rendering equation. You need a coherent grammar of visual presentation that is pleasing to the eye. The engine can facilitate this if you know what you want but it cannot make anything awesome by itself.