First differences I consider to be important (of course, the one that runs throughout the entire LXX is that YHWH never appears as YHWH, it is always "Lord"):
Genesis 2:18, LXX (NETS):
Then the Lord God said, "It is not good that the man is alone; let us make him a helper corresponding to him."
Genesis 2:18, MT (NWT):
18 And Jehovah God went on to say: “It is not good for the man to continue by himself. I am going to make a helper for him, as a complement of him.”
Comment: Eve was made with help in LXX, only God made Eve in the MT.
Also:
Genesis 2:19, LXX (NETS):
And out of the earth God furthermore formed all the animals of the field and all the birds of the sky and brought them to Adam to see what he would call them, and anything, whatever Adam called it as living creature, this was its name.
MT (NWT):
(Genesis 2:19) 19 Now Jehovah God was forming from the ground every wild beast of the field and every flying creature of the heavens, and he began bringing them to the man to see what he would call each one; and whatever the man would call it, each living soul, that was its name.
Comment: Adam doesn't appear in MT until Genesis 3:17, but appears in LXX in Genesis 2:19.
Genesis 2:23, LXX (NETS):
And
Adam said, "This now is bone of my bones and flesh of my flesh; this one shall be called Woman, for
out of her husband she was taken."
Genesis 2: 23, MT (NWT):
Then
the man said:“This is at last bone of my bonesAnd flesh of my flesh.This one will be called Woman,Because
from man this one was taken.”
Comment: Different meanings in the LXX vs the MT.
Genesis 3:5, LXX (NETS):
for God knew that on the day you eat of it, your eyes would be opened, and you would be like
gods knowing good and evil."
Genesis 3:5, MT (NWT):
(Genesis 3:5) 5 For God knows that in the very day of YOUR eating from it YOUR eyes are bound to be opened and YOU are bound to be like
God, KNOWING good and bad.”
Comment: HUGE difference in theological implications. In the LXX, there is the implication that there are many gods, and that once you become a god, you know good and bad. In the MT there is the implication that only God knows what's good and bad.
Genesis 3:10, LXX (NETS):
And he said to him, "I heard the sound of you
walking about in the orchard, and I was afraid, because I
am naked, and I hid myself."
Genesis 3:10, MT (NWT):
10 Finally he said: “Your voice I heard in the garden, but I was afraid because I
was naked and so I hid myself.”
Comment: It is possible that the WT tries to hide the more anthropomorphic version of God in the LXX, since in the LXX God is walking about in the garden.
Genesis 3:15, LXX (NETS):
And I will put enmity between you and between the woman and between your offspring and between her offspring; he will
watch your head, and you will
watch his heel.
Genesis 3:15, MT (NW):
15 And I shall put enmity between you and the woman and between your seed and her seed. He will
bruise you in the head and you will
bruise him in the heel.”
Comment: Quite a different thing! One thing is to watch someone's body part, and another to bruise it!
Genesis 4:5-7, LXX (NETS):
but on Kain and on his offerings he was not intent. And it
distressed Kain
exceedingly, and he collapsed in countenance. And the Lord God said to Kain, "Why have you become
deeply grieved, and why has your countenance collapsed?
If you offer correctly but do not divide correctly, have you not sinned? Be still; his recourse is to you, and you will rule over him."Genesis 4:5-7, MT (NWT): 5 he did not look with any favor upon Cain and upon his offering. And Cain
grew hot with great anger, and his countenance began to fall. 6 At this Jehovah said to Cain: “Why are you
hot with anger and why has your countenance fallen? 7
If you turn to doing good, will there not be an exaltation? But if you do not turn to doing good, there is sin crouching at the entrance, and for you is its craving; and will you, for your part, get the mastery over it?”
Comment: COMPLETELY DIFFERENT! In the LXX, it seems like God liked the offering but not how it was split, and it seems like God is saying to Cain, "don't worry, you will rule over Abel at the end of the day". Cain was portrayed as being saddened, even grieving. In the MT, Cain is portrayed as evil and angry and has an anachronism, where animals are supposedly man-eaters before the flood.