"Noach was a righteous man, pure in his generation" (Bereishis 6, 9). Rashi writes that some (of Chazal) explain this pasuk in a positive light, while others explain it derogatorily. Those who explain it complimentarily, assert that had Noach been in a generation with other righteous people he would have been an even greater tzaddik. However, those who explain it derogatorily posit that only in his generation he was considered a tzaddik, and had he lived in the generation of Avraham, he would not have been given even an "honorable mention."
Rav Wolbe (Shiurei Chumash) quotes Rav Yeruchom Levovitz zt"l who stresses the Torah's perception of man's accomplishments. Though some explain the Torah's accolade as a true compliment and some explain it only in relation to Noach's generation, they both agree that one is measured with a yardstick in comparison to the generation of the greatest stature. For example, one can measure the amount of light produced by a candle in comparison to a lightbulb or flashlight, or in comparison to the greatest source of light that exists - the light of the sun. The Torah gauges one's spiritual level in comparison to the light of the "sun" - the founder of Judaism, Avraham Avinu.