Many fusions, such as Garnet and Stevonnie, are stable fusions full of care, trust, and love, whereas some fusions, such as Malachite, are full of anger and hatred! For many Gems, Fusion is the ultimate bond between two or more Gems, but for many other Gems Fusion is just a war technique, and Homeworld Gems seem to think of fusion between different types of Gems as "disgusting".
Most Fusion Gems have a unique appearance, but some Gems such as Ruby (Fusion) appear and act the same as their components, only changing in size. This is due to the fact that the Fusion was formed between Gems of the same type.
Most fusions have their own personality, though there are some exceptions such as Ruby (Fusion), due to the fact that her components have similar, or even the same, personalities, and Malachite, due to her unstability, she is controlled by Lapis or Jasper instead of both at the same time. Fusions' personalities are as unique and special as those of normal gems.