JOEL - It was not necessesarily the same kind of manifestation. Here are the relavent scriptures:

"And never have I showed myself unto man whom I have created, for never has man believed in me as thou hast. Seest thou that ye are created after mine own image? Yea, even all men were created in the beginning after mine own image.
Behold, this body, which ye now behold, is the body of my spirit; and man have I created after the body of my spirit; and even as I appear unto thee to be in the spirit will I appear unto my people in the flesh." (Ether 3:15-16)

"And I(Enoch) saw the Lord; and he stood before my face, and he talked with me, even as a man talketh one with another, face to face; and he said unto me: Look, and I will show unto thee the world for the space of many generations." (Moses 7:4)

"And Adam and Eve, his wife, called upon the name of the Lord, and they heard the voice of the Lord from the way toward the Garden of Eden, speaking unto them, and they saw him not; for they were shut out from his presence." (Moses 5:4)

We know by the Ether scripture that the "God" the Brother of Jared saw was deffinately Jesus Christ in His pre-mortal state. The Moses scriptures suggest that Enoch and Adam both saw God as well.
In Adam's case, the scriptures say that he walked and talked with God, but this was when Adam was in a pre-mortal state and required no belief or faith; so the circumstances were different compared to the Brother of Jared who was mortal.
In the case of Enoch and other prophets, perhaps the Lord never revealed his complete bodily image as He did for the Brother of Jared. Previous prophets may have only seen the face of God or some other form that represented God's presence.
Also, in the past, prophets such as Enoch and Moses had to be spiritually prepared and be invited to see God. This was not the case with the Brother of Jared. His faith was so strong that the Lord could not keep Himself from being seen by him. This had not happened with any other prophet before.