was a man of obvious intelligence, able to move incredible numbers of troops with lightning speed against incredible odds. But he did have a few downfalls;
Arrogance - Though this could be called a fault, many of his military victories would not have been won without a certain amount of unforgiving arrogance.
A strange illness often labeled as epilepsy
Though Caesar's own journal never makes mention of his illness, he does hint to it. He might say, "Caesar was forced to take leave.." or the such, to cover up the fact that he was incapacitated. Many historians and servants that recorded events, however, record strange fits of migraine headaches and loss of consciousness or seizure.
Plutarch of Chaeronea trans. by Robin Seagar.
"Caesar was not present personally at the action:
he began to suffer from an attack of his usual illness
just as he was drawing up his troops and ordering them to
their positions, and, being aware at once that the illness
was coming on, and finding that he was already losing the
use of his faculties, he was carried, before they entirely
left him, to a tower nearby, where he rested while the
battle was going on."
"For he was a slightly built man, had a soft and
white skin, suffered from headaches and was subject to
epileptic fits. (His first epileptic attack took place, it
is said, in Cordoba.) Yet so far from making his poor
health an excuse for living an easy life, he used warfare
as a tonic for his health. By long hard journeys, simple
diet, sleeping night after night in the open, and rough
living he fought off his illness and made his body strong
enough to resist all attacks."
Epilepsy - 'Epilepsy is characterized by seizures of any type that occur on a chronic, recurrent basis and have no known cause. In addition to seizures, there may be other symptoms or signs, such as headache, changes in mood or energy level, dizziness, fainting, confusion, and memory loss.'
As CloudStrife mentioned in his writeup: The Death of Julius Caesar, a man theorized Caesar had himself killed on the basis that he was aged and suffering from incontinence. Epilepsy causes memory loss, seizure, headaches, all with unknown cause. This could be the basis for that theory, although I believe that Caesar was such a truly ambitious, power-hungry individual that he would rather gladly rule as a shell than die as a soldier.