Positive or negative characteristics about any political leader depend on the point of view of the person evaluating the leader, including Che Guevara. There are many who would say he had no negative characteristics, while others would have serious concerns about some of his attitudes and actions. You will need to decide how you interpret his actions.
Che Guevara fought with Fidel Castro to overthrow the United States-supported Cuban dictator Fulgenico Batista in 1959. After the Revolution, Guevara served various roles in the new government. He reformed agriculture by ending large privately-owned plantations, distributing land in smaller parcels to private individuals or keeping it in government-owned communes. He oversaw the execution of many officials from the Batista government. He worked tirelessly (some would say ruthlessly) to promote the development of a communist socialist economy in which all citizens would work for the good of the society and all would be rewarded equally. As a key diplomat in dealing with the Soviet Union, Guevara was instrumental in arranging for the importation of Soviet nuclear-armed ballistic missiles to Cuba, precipitating the Cuban missile crisis in October, 1962.