A lot of series out there has sequels. And, unfortunately, most times they aren't good and they are unnecesssary. I promised you the moon isn't completely necessary to complete the story or to resolve isssues left from the 1st season. But, actually, is a really good sequel which compliments I Told Sunset about You. The 2nd season lets us to explore more the characters and their story more, their journey of growing up, finding and understanding themselves. Their relationship is a realistic relationship betweem to young people who are starting to discover and see the reallity of the world and sometimes the people change. Nothing stays the same and we have to understand that.
In reallity, I enjoyed more the 2nd season (maybe because my age is nearer to the age of Teh and Oh-aew in the 2nd season), even if I think is a lot more heavy in angst.