The pasuk says that Noach was a Tzadik, a righteous person, in his generation. Rashi writes that there are some Rabbis that explain the emphasis of the word his generation as praise; if Noach would have been in a generation of Tzadikim he would have been even more righteous. Other Rabbis explain this as a negative attribute; Noach was only considered righteous relative to his own generation but had he been in a generation with someone like Avraham he would have not been considered special.
Both of these opinions have a difficulty in them. For the praise side, Rashi says right after this, that Noach needed support from Hashem while Avraham was able to be righteous in his merit. Clearly, Noach was less worthy than Avraham. And for the negative side, how can we speak negatively about Noach if we have the option of praising him.
The answer is that there really isn’t any argument here. There are just two aspects to Noach, and indeed, to all Tzadikim. Everyone is in agreement that Noach did righteous deeds and was a Tzadik in his own merit. However, the main purpose of good deeds is to acknowledge Hashem’s presence in the world and to bring about an awareness of Hashem’s complete control of every aspect of existence. The goal is to bring others to do good. In this regard Avraham excelled and Noach failed.
Avraham went around the world loudly announcing the existence of Hashem and bringing people closer to His worship. And indeed Avraham is considered the founder of monotheism, the key belief in Judaism that there is one God who created and continues to create this world from complete nothingness into the full existence that we experience. Noach on the other hand was only able to save himself and his family. He was not able to rescue his generation by bringing them to Torah and helping them repent from their sinful ways.
Perhaps one might ask that doesn’t this prove that Avraham was objectively greater than Noach? The answer is that in order to change the world on the scale that Avraham did, he needed the power of the Torah. He needed the Torah to be able to show people the truth about the universe and to guide them in the right ways. It is brought down in the Gemara that the age of Torah began during Avraham’s lifetime. So Avraham utilizing the power of Torah was able to change the world while Noach who was before that time was able to change his own ways but not to have an effect on the world.