This is gonna sound controversial to some but, on the whole Castro's legacy was positive. I am looking at this from the perspective of someone from the Global South. 
(i)He assisted Nelson Mandela in the fight against Apartheid. 
(ii)In my country(Jamaica) he played a pivotal role in sending doctors and helping in land reform. 
(iii)He supported anti imperialist and anti colonial movements globally, but especially in Africa. 
(iv)Though he was an atheist, he supported Liberation theology in the 80s which included his relationship with Fr. Ernesto Cardenal in Nicuragua. 

He was authoritarian and I want Cuba to be a democracy. I am also critical of his treatment of Cuba's LGBT population and his suppression of dissidents. But I think on the whole the balance sheet shows more positives than negatives.