The Brazilian Olympics were a failure for many reasons. First of all, the Brazilian fans were uncivilized and rude... Booing athletes from other countries throughout numerous events. The olympics are supposed to bring countries together, not bring athletes to foreign countries only to have them ridiculed by the hosts.
Brazil also has a lower HDI than Iran according to 2015 Human Development Index numbers... If it's that low, why is a country that needs to be investing in internal infrastructure paying billions of dollars to host international events? It's looking to gain some international attention in the positive light, which was a failure because the only attention Brazil was getting was how rude their fans were, how dangerous the city was at night, and the looming fear of Zika.
Lastly and most importantly, the Brazilian Olympics were a failure because of how many empty seats there were. There are 200 million+ people living in Brazil, yet most couldn't afford tickets to see any events let alone pay for transportation, food, lodging in order to attend one event let alone many. Additionally, the threat of robbery and violence in addition to the threat of Zika virus prevented many international travelers, who otherwise would fit the expense of traveling for the olympics, avoided it altogether. Thus Brazil is a failure and should be ashamed of itself.