Unity scales really nice, from very tiny small games to gigantic MMO games. It doesn't mean that you'll be able to create those games but if you have the sources (money and skilled team) yes!
Regarding graphics, Unity give you direct access to hardware, you can use OpenGL inside Unity, create any kind of shading and effect, create your own lighting model, whatever you want (if you can).
You can extend the Unity editor and create your own specific tools. For example we have our mission (well objective/quest) editor, dialog and item system hooked in the editor with other tools, they are all part of our our own framework (FOG which stands for Fear Oriented Gameplay). Unity is simply amazing and powerful. The upcoming Unity4 will have support for Directx11 (with many other great new features/additions). We are private alpha and beta developers of Unity, we give direct input/feedback to them every day, they made changes on Unity based on our feedback/suggestions and they are the coolest developers on earth!
PS: We are already using Unity4 on Forgotten Memories!