"Noah Tzadik Tamim Haya Bedorotav." "Noah was righteous and perfect in his generations." Gemara Sanhedrin and Medrash Tanhuma which Rashi brings, shows that Rabbi Yohanan is not so impressed by these praises of Noah. "In his generations he was righteous, but not in other generations." "Had Noah been in the generation of Abraham, he would not be considered righteous at all." "Resh Lakish, however, is extremely impressed." Even in his generations which were corrupt, he was righteous. How much more so if he lived among other righteous people.

The Mishnah in Pikei Avot strongly suggests that we should judge everyone favorably (Avot 1.6). Why then does Rabbi Yohanan exercise the opposite? Furthermore, the Torah carefully describes Noah as Tzadik and Tamin in his generations - many generations - a praise no one else merited before or after him. veNoah matza hen beinei HaShem - Noah found favor in the eyes of HaShem. Ki otcha raiti tsadik lefanai bador hazeh - For it is you that I see to be righteous before Me in this generation.

So, if HaShem praises Noah to such a degree, why should some of our sages be critical of him?

It is a well-known idea that each tsadik is judged in accordance with his contemporaries. "Yiftah in his generation is like Samuel in his generation" say our sages. Each leader of the generation is as great as Shmuel, Aaron and even Moshe (Rosh Hashana 25A).

Rov Yohanan, in my opinion, is not being critical of Noah. He is simply saying that Noah, in his generations, was a Tzadik, just as Yiftah was considered an important leader of his generation, as important as even Shmuel HaNavi. Noah was not as great as Abraham. So, had he been in Abraham's generations, he would be insignificant. Just as Yiftah, if he had been in Shmuel's generations, he would be insignificant. Just as Yiftah, if he had been in Shmuel's generation, he too would have been insignificant and perhaps that is the reason why the Torah praises him and emphasizes the word "Bdorotav," in his generations.
Mayenah shel Torah quotes Pardes Yossef who gives a different and perhaps a Hassidic answer. He explains that those who criticize Noah do so from an intuition that all Tsadimim will inevitably have Misnagdim, those who vehemently oppose them. Even Moshe Rabeinu had his Misnagdim. Here, they teach us that even the first mentioned Tzadik (Noah) in the Torah is liable to criticism. So, when we see a Tzadik criticized by some, we must still consider him a Tzadik as long as he has others who praise him.

Another puzzling Rashi (7.8) is when he writes that Noah and his family came to the Ark Mipnei Mei Hamabul - because of the Flood. This shows that Noah's faith was weak; he believed and did not believe (he was doubtful) that the Flood will come. He did not enter the Ark until the water forced him to. How can Noah be accused of such a lack of faith? Had he not spent 120 years building the Ark? Was not the building of the Ark for such duration so that others will repent? Should we not judge him exactly the opposite and say that Noah continued to hope until the last minute that Hashem will have compassion and not bring the Flood?

In Sefer Degel Hamussar by Rabbi Gershon Libman of Novardok at Yeshiva Or Yossef on France, I found an interesting Mussar answer to this question. He explains that there, the Torah and Rashi are trying to emphasize that even a great Tzadik may be influenced by the people of his generation. Although he occupies himself in teaching and Kiruv as Noah did for 120 years, he exposes himself to negative influences of those whom he tries to reproof. This influence may sometimes cause the Tzadik to doubt his own mission. Yes, Noah found favor in the eyes of HaShem. On the other hand, he may have had his faith compromised by those who lacked faith in HaShem.

Noah may not have been as great as Abraham who saved many souls, �kol hanefesh asher assu beharan�, and prayed for Sodom and Amorah. But Noah could have been greater if he were not surrounded by so much corruption.