There is an obvious question: The Torah calls Noah "sincere", and we have Hashem telling Avraham "be sincere". Evidently, Noah has a quality that Avraham does not? Therefore our Hakhamim deal with this textual problem in the following Midrash brought down by Rashi.
Note: These two opinions on the character of Noah (one saying he would have been a better person in a righteous generation, and the other saying he would be regular) only disagree on the potential he might have had if he lived in a righteous generation. But they both agree that his righteousness can at best be described as mediocre.
The contrast between Noah and Avraham is further understood by their differing reactions to a similar situation. Noah and Avraham were both warned about the destruction of mankind by Hashem:
When Noah was told about the destruction of world in the following Pasuk :
Avraham on the other hand reacted a little differently:
We can also reanalyze the first 2 Pesukim that we brought down;
On the other hand, in regards to Avraham the Passuk uses a different language:
Noah and Avraham were two very important men in the history of mankind, who were charged with two very different missions. The mission of Noah was the mission of survival. The world was at a cross roads that needed to be fixed, and Noah stepped up the the plate and ensured the survival and continuation of mankind. In that way he "walked with god" and kept the status quo alive. He paved the way for a person like Avraham to emerge armed with the mission of spreading God's word, and "walk in front of Hashem"