Most are for the active conservation of vulnerable species and the level of education provided by the zoos are usually very high. From gestation period to sources of threats in the wild, information about different species are varied, abundant, and usually displayed in multiple languages (usually English + local language).
The zoos I rate highly have exceptional facilities with large enclosures and a good layout/map. These aspects come together to provide the visitor with a pleasant experience and the animals with plenty of space to roam.
TLDR: conditions are very acceptable (as far as I know) but as my family dislikes the primate exhibits I am unsure about the bananas question.