I feel like there can be a tendency to evaluate great generals through the lens of their great battles, such as Alesia or Pharsalus for Caesar and Zama for Scipio Africanus, but the ability to win a battle is only the tip of their abilities. What Caesar, Scipio, Pompey, and Sertorius (I'll leave Belisarius out of this because I am not nearly as familiar with his campaigns) had in common was an ability to mobilize local support and thus keep their armies reinforced, fed, and paid while far from Rome. These generals relied on patron-client relationships throughout the empire and even beyond it to do so.

Sertorius and Africanus, in fact, both relied on connections with the Celtiberian tribes in Hispania for what are arguably their greatest successes. It is important to keep in mind that Hispania was not fully brought into the Roman fold until the reign of Augustus, over two centuries after the first Roman armies arrived in Iberia. The generals who operated there could not assume support from Roman citizens, but had to earn it through alliances, gifts, and victories. While Hannibal rampaged through Italy, the Scipio family (Africanus, after his father and uncle were killed) coordinated Roman efforts to defeat Punic forces in Spain. And Scipio Africanus did so brilliantly- despite the decades long Barcid head start in the region, he was able to pull together enough alliances to support his army and win several decisive victories. Without the seizure of Carthago Nova in 210 and the Battle of Ilipa in 206, Zama doesn't happen at all.

But while Scipio Africanus was willing to step back into relative obscurity after Zama, having well served the Republic, Sertorius relocated to Hispania after the collapse of Cinna's Populares faction in Rome, and saw himself as more legitimately Roman than Sulla's Optimates- who then sought to destroy Sertorius. He earned the respect of the Lusitanians (in modern-day Portugal) who desired a strong leader and offered him the position. Thousands of Lusitanian warriors, according to Plutarch, offered him the devotio ibérico, a bond of service unto death along a very similar vein to the fictional Dothraki blood riders. And Sertorius successfully waged a guerrilla war against far more numerous Roman forces for eight years, led by a young Pompey.

As far as the loss of his eye... who knows? Plutarch says that "he exposed his person unsparingly in battle" which likely means that he led from near the front, within range of enemy missiles but not in too much danger (until one happened to hit him in the face) or he could have waded into the melee on occasion. If any Roman general would have done that, it may as well be Sertorius with a nearly unparalleled reputation for bravery.

So what separates Sertorius from these other generals? Not much, except that they are not painted in the histories as traitors to Rome who essentially became foreign kings. He had bravery, charisma, diplomatic acumen, and a strategic mind comparable to the rest. He was in incredible threat, not in the sense that his Lusitanian kingdom/proconsulate posed a serious threat to Italy, but instead that he was one of the first Roman generals who "went rogue", a theme that would become fatally common in the last century of the Republic due to the increasing political factionalization.