And God saw everything that he had made, and behold, it was very good. And there was evening and there was morning, the sixth day.
And the Lord was sorry that he had made man on the earth, and it grieved him to his heart.
The Claim: In Genesis 1 God was pleased with his creation, but in Genesis 6:6, God was displeased with his creation.
The Explanation: There are two major ways to show how this is not a contradiction. First of all, it's important to realize that there was a gap of time in between Genesis 1:31 and Genesis 6:6. Once you realize this, the logical question becomes: Is it possible to be pleased at one point in time, and then displeased at another point in time? The answer is obviously yes, so there's no contradiction.
The second thing to note is Genesis 6:6 is taken out of context. Genesis 6:6 leaves us with the looming question of, why did God become displeased with his creation? The answer is found in the preceding verse.
The Lord saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually.
In Genesis 1:31, God was pleased with his creation of man, and likewise, man was not wicked at this time. I mentioned earlier that there was a period of time that elapsed between Genesis 1:31 and Genesis 6:6, and there were events that took place during that timeframe. Most notably, we have the fall of man in Genesis 3, where man begins to disobey God. By the time of Genesis 6:5, the disobedience has become so great that God became displeased with man. There's no contradiction here either.