Like most things the EU is not a black and white entity. These are some of the good things that come to my mind:
It brings together a large number of countries, closely allying them, interlinking them through trade and enabling them to talk, share and understand each other. I believe that close contact prevents friction and reduces the possibility of war.
It produces frictionless trade.
It enables free movement of people between countries and gives people the opportunity to study, work and travel easily.
It is powerful as a bloc – giving greater voice to the rest of the world.
It creates an outward looking society that encourages respect of other cultures and counters that insular feeling that can so easily develop into a feeling of superiority and arrogance.
It enables much productive collaboration between nations and enables funding of bigger projects. It brings together a wider range of talents from which science, technology and business benefit.