One of the best critiques addressing some of their systemic failings is that of the thinker and philosopher Slavoj Zizek. His core point is that charities do not seek to address the causes of povery, disease, ignorance etc focusing on the emotive effects. His RSA talk is summarised in the following video:
Professor Ilan Kapoor's "Celebrity Humanitarianism" is another excellent work which critiques spectacularized humanitarianism, images of stars doing relief work or posing with newly transnationally adopted children; "benevolent" corporate billionaires on redemptive missions in Africa; or iconic manoeuvres of semiotically savvy NGOs. His Zizekian analysis applies to humanitarianism in general whereby it legitimates and promotes liberal capitalism and perpetuates global inequity.