Why does the Eastern Orthodox Church dislike the idea that the Spirit proceeds from the Son?

In studying the Orthodox doctrines I have noticed that there is controversy about the nature of the Spirit and that the word 'filioque' is tossed around. What I am wondering is, what is the underlying concept whereby Catholic and Protestant ideas about the Trinity conflict with Eastern Orthodox? What is the real issue that keeps Orthodox on their own with respect to the Spirit proceeding from the Father only and not from the Son?