The primary qualities of a good video animator are creativity, patience and stamina. A good video animator is creative in their use of form, motion, colour and their myriad stylistic approaches to narrative. It takes patience to craft the story within an allotted time frame while not missing any important story beats. And it requires stamina to keep your eyes on the screen for hours at a time as you add in those final touches or so that your weary and sore back can heal through sleep.
It's also important for a good video animator to have strong visual imagination with respect both to how they create graphics digitally with light software like Photoshop.