Jonathan Parshall:

Perhaps Japan's most gifted carrier admiral, Yamaguchi was astute, aggressive, and ambitious. Unfortunately for Japan's war effort, he was also heavily steeped in the Bushido Code, which meant that he was pretty much obligated to do away with himself after having lost his carrier Hiryu during the closing stages of the Battle of Midway. So it goes.

C. Peter Chen:

Near the end of the Battle of Midway, he told pilot Tomonaga, who was about to go on an attack in which he did not expect to return, 'I will gladly follow you'. That summed up his deep belief in that he must succeed, or would die trying. Instead of taking the chance to escape with Hiryu, thus potentially saving a fleet carrier to fight another day, he steered Hiryu into more dangerous waters for a final attack that was nearly impossible to win. Before Midway, he was considered capable, brave, and a possible successor to Yamamoto; after this demonstration of stubborness, it showed that he might not had been a good choice as Yamamoto's successor, after all.

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WW2DB biography of Tamon Yamaguchi