Well, yes He did receive His "humanness" from the Theotokos but the Theotokos was sinless by grace and the 2nd Eve, a pre Fall Eve. The human nature which Christ took on was a pre Fall nature, as I said. +Gregory Palamas wrote:
"Through the fall our nature was stripped of divine illumination and resplendence. But the Logos of God had pity upon our disfigurement and in His compassion He took our nature upon Himself, and on Tabor He manifested it to His elect disciples clothed once again most brilliantly. He shows what we once were and what we shall become through Him in the age to come, if we choose to live our present life as far as possible in accordance with His ways."
This of course is not to say that when Christ took on flesh, He did not suffer. The Bible and the Fathers assure us of this and it is quite apparent that a) He took on that suffering, that pain of humanity, quite willingly and b) that it was the will of the Father that He do so.
"O Savior of all men, especially of those who have faith, Because Thou wast crucified of Thy own will, and was put to death voluntarily, The lawless say not of their will Were the limbs of the robbers broken; But Thine, they did not break, in order that they might learn That Thou didst not come among the dead against Thy will, But willingly Thou didst give up Thy spirit, Thou Who art everywhere and fillest all things." +Romanos the Melodist
And if we want to become like God, we have the opportunity and the ability through grace to do the exact same thing.
To tell the truth, whether Christ assumed a fallen or unfallen human nature is a question that I hadn't really given any thought to until the discussions on this thread.
Doing a little on-line looking around, I found that there is a nice section in this article that maintains quite strongly that the Patristic tradition is indeed exactly what you say: namely that he assumed unfallen human nature. Not that I ever doubted you! :-)
The most interesting quotations from the section were:
"...the perfectly Orthodox view set forth by St. John of Damascus: that in assuming human nature, the Logos also freely assumed what St. John calls the "unblameworthy passions," such as "hunger, thirst, weariness, labor, tears, decay, shrinking from death, fear, agony with the bloody sweat, succor at the hands of Angels because of the weakness of nature, and other such like passions which belong by nature to every man" ("Exact Exposition of the Orthodox Faith" III.20)"
"Father [Georges] Florovsky, for example, asserts that "in the Incarnation the Word assumes the original human nature, innocent and free from original sin, without any stain." "This," he continues, "does not violate the fullness of nature, nor does it affect the Saviours likeness to us sinful people. For sin does not belong to human nature, but is a parasitic and abnormal growth" (Creation and Redemption)"
"Vladimir Lossky, for his part, following St. Maximos the Confessor (Questions to Thalassios, 21), states that our Lords humanity "had the immortal and incorruptible character of the nature of Adam before he sinned, but Christ submitted it voluntarily to the condition of our fallen nature" (The Mystical Theology of the Eastern Church). Like St. John of Damascus, Lossky emphasizes that Christ voluntarily experienced the infirmities of our post-lapsarian nature; He did not assume an infirm nature. By His human will, Christ "accepted what was contrary to incorruptible and deified humanity"—that is, the unblameworthy passions (ibid., p. 148). There is, therefore, no contradiction between the assumption by Christ of unfallen human nature and His acceptance of the physical consequences of our fallenness."