Lens performance simply does not get any better. Just read the name, and you should already know that this lens means business. Amazing image quality that beats any zoom and places itself among the top of fixed focal length lenses. It is the ultimate portrait lens for both indoor and outdoor. Especially useful in weddings when taking formal portraits of the bride/groom getting ready in her/his room. Take advantage of its large aperture performance while you can so you can enjoy the excitement of noise free images! It is the king for those who want the maximum f/stop creativity.
Physically this lens could have been built better. The lens should not have to be mounted on the camera to activate manual focus. This is not severe in most situations, but the fact that this lens also extends externally, makes me want to return the lens to infinity when I am finished for the sake of reducing the lens size. I am also quite surprised that a lens at this level does not get weather sealing! Though not very important, its a member of the L class, why not have it! AF speed is decent, but not fast enough for sports and quick stage photography. But this lens was never really meant for such action anyway.
I don't recommend large aperture lenses like these for beginners or for those who are not careful with focusing. With such a shallow depth of field, you really only get one thing sharp. The rest would be soft. Even the slightest wrong movement can render a soft image. I have been told by Canon reps and agree with them that "Focusing is an acquired skill". This lens would really test that skill.