As stated in Genesis 6:8 (kjv) But Noah found grace in the eyes of the LORD.
It is answered in the next verse, as well as the first verse of Genesis 7:
9 These are the generations of Noah. Noah was a just man and perfect in his generations, and Noah walked with God.
1 And Yahveh said to Noah, “Come, you and all your house into the ark, for I have seen you righteous before Me in this generation.”
I think the bible is clear; Noah pleased God because, just like Abraham, he believed God and it was accounted to him for righteousness. Without faith, it is impossible to please Him.
Hebrews 11:6-7 (KJV)
6 But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him. 7 By faith Noah, being warned of God of things not seen as yet, moved with fear, prepared an ark to the saving of his house; by the which he condemned the world, and became heir of the righteousness which is by faith.