The opening of Parshat Noach starts off by telling us that Noach was "a righteous man, perfect in his generations," (Bereshit 6:9). Rashi states that this is a rebuke of Noach, who was only righteous in his generations due to the ways of his contemporaries (Sefer HaParshiyot states however that the righteous of each generation must be judged in terms of their own times).
Later in the parsha, Noach is told, "Make for yourself an Ark of gopher wood," (Bereshit 6:14). Rashi's view of Noach is accepted by the Alshich, who sees this as a rebuke of Noach, "Make an ark to symbolize your own behavior. You remained aloof from your compatriots, instead of chastising them and trying to save them by improving their conduct. Now you will isolate yourself in an Ark with beasts and animals."
Further criticism of Noach comes from Isaiah, who actually calls the Flood "waters of Noach," (מי נח, Isaiah 54:9) due to Noach's failure to even try to influence his generation. The Zohar even implies that Noach was responsible for the Flood (which confirms the awesome responsibility Tzaddikim have).
Noach's actions present us with an important lesson - one must strive to live a righteous life that can affect his surrounding environment for the better. Unlike Avraham Avinu, who came ten generations later, Noach's righteousness was essentially hidden from the masses, depriving a needing world of his positive influence and guidance.
(Ideas taken from The Stone Edition Chumash)