As someone who's passed his first set of ATPL's, and really should be revising right now for the last of my second set, I'd say the most important aptitude to actually pass the exams is to have a photographic memory for feedback.
Also, the ability not to think too deeply about some of the answers to the questions they ask.
Perseverance is the name of the game here, not bits of meaningless papery things like degree certificates.
Bring on Air Law at 9am tomorrow!