What are the strengths and weaknesses of the united nations?

 Briefly: the strengths are the individual UN agencies, like UNICEF, UNIFEM, UNHCR, UNFPA, UNESCO, WHO, WFP and others that are doing important, great work helping millions of people. These agencies are largely independent, and that's a strength as well. Look up each agency, and you will see incredible work. To me, these agencies represent the best about the UN. 

The weaknesses: the UN Security Council permanent membership is too limited and, in this day and age, makes no sense. There are countries that should have a voice as permanent members, based on their huge investments in UN projects, as well as the populations they represent, but they are locked out, and there's no meaningful effort to give them that voice. The employment system for UN agencies needs revising -- specifically, it needs to be easier to fire *anyone*, no matter how long he or she has been at the agency or what country he or she represents. The UN General Assembly is nothing but a blah blah shop - all resolutions are non-binding, and nothing it says is really listened to. The UN Peace Keeping operations should be more transparent in terms of what country's military are operating where, and when they violate international law, that military should be identified by country -- no more hiding behind the "UN Peace Keeper" moniker. Finally, the UN does an extremely poor job educating people in the USA about what it does, and what it DOES not and CANNOT do.