Wade St. Onge has been reading about the alleged Medjugorje apparition for some time, and has written a seven-part series about the case for his theology blog.
He reviews commonly posed arguments for and against the phenomenon and makes distinctions among the stronger and weaker elements in each case. St. Onge does not always put emphasis where I would, but is trying to be balanced. For readers not familiar with the controversy, I think his article will be a good introduction to the subject.