Orthodoxy does believe in mystery. This is because "the foolishness of God is wiser than man's wisdom" (1 Cor 1:25 NIV).
Therefore, all language that is applied to Him must be inexact at best, heretical at worst. Mystical theology may have started with Clement of Alexandria (d. 215), so it is not new.
In the West, especially with Thomas Acquinas, thinkers tried to define everything. Modern examples include the cessation of the sign of the cross by Protestants and the doctrine of transsubstantation by the Roman Catholics. No definitions are better than inaccurate ones.
Now, does this mean Orthodox have little theology? No. IMHO, Orthodox theology is best and it's been around a long time. Just because we (like Paul) believe in mystery, doesn't mean we don't think. There are modern theologians (like Alexander Schmemann, Vladimar Lossky, Thomas Hopko) and ancient ones (Gregory Palamas). The idea, based on Cyril's thought, is not to limit God by defining Him, but eliminating incorrect descriptions of God. (This is called apophatic theology). The Ecumenical Councils did just this. They prohibited weird descriptions of the Trinity, such as Jesus being a created being (Arianism).
Take it from me, Orthodox think a lot about God, but reason only goes so far. Mystery must take over at some point, because of what Paul said: the wisdom of man is nothing compared with God.
Hope this helps.