The difference between Charms and Transfiguration
A charm adds properties to an object or creature. Transfiguration however, alters the object or creature completely.
The larger the creature or object, the harder it is to transfigure.
Transfiguring oneself into an animal is completely different from becoming a full-fledged Animagus.
5 exceptions of what elements one cannot transfigure by use of magic: food, love, life, information and money.
The opposite of Transfiguration is Untransfiguration.