On balance it is better to have the UN than not. It's efforts at peacekeeping have not all been bad, although from the essay you'd guess it was bad, bad.

How about including references to the successes: Namibia, Mozambique, Cambodia, Cyprus and on Israel's borders?

The UN is generally only successful in conflicts when there is a local and international agreement. The UN's mistake IMO was to try peace enforcement when only international agreement was in place, the DRC is a great example.

You will have noted the changing composition of UN military forces too, many of the "regulars" are no longer there: Canada, Scandinavia, and even India appears to be asking itself why. The USA rarely has been a participant.