Caesar does not strike me as a battlefield wizard a la Alexander, but he was a genius of a general. In his day, and verily through to today, generals do more than just direct a battle. In the period before him, most generals were indeed simple battlefield commanders. By caesar's time, they were more and more involved with directing the entire war effort at an operational scale.
In this, Caesar did excel. He chose when to fight (as was standard for the day), where to fight (as per standard) but also often forced the enemy to meet him on a field of his choosing or used his famed speed to move and attack an enemy where he was not prepared to fight. He used his recon assets (Aedui cavalry, among others) better than most generals of his day, and used their intelligence to strike swiftly and deeply where it would hurt the most. His few defeats/draws were results of miscommunication or disobedience (Gergovia), adapting to new or unorthodox tactics and weapons (Britannia, though he figured out a counter quicker than most Roman generals would. Rome had a long history of losing the first battle against any new foe), or bad luck (Dyrrhachium, where Gallic deserters gave good intel to Pompeius).
His charisma and charm were legendary- and any good general needs the love and support of his men in order to make them perform miracles. Alexander had this, Pompeius (when he was younger) had it, but Caesar had it in barrels and tons.
Legions themselves were capable of winning battles as the documentary says- they did not need brilliant men to lead a war machine, and the sheer number of battles fought by the Roman army versus the percentage of brilliant men available provides ample probability that many commanders must have been of mediocre quality. Some, like Caepio, were in fact militarily incompetent, while others, like Sulla or Marius, were exceptional. Suetonius was frikkin lucky that the Britons assaulting his position on Watling Street were so thoroughly unorganized- all he had to do was order his legions into wedges, then let them do their thing. Varro found out the hard way that legions left to 'do their thing' can lead to disaster (Cannae).
But saying Caesar was no genius of a general is damned near insulting. He might not have been a genius on the tactical side, but he outshone every man of his time in the art of generalship.