Do not like Dan Humphrey. Gatsby is great because he died, his American dream broke up and his innocence does not lose while Humphrey is totally on the contrary. Marrying Serena is totally not a good ending. Dan is supposed to be not “one of us” ever.
Being good with Blair is the start of Dan Humphrey getting in, bur he could never be truly together with Blair . Blair is the real typical one of the upper east, who was with Dan just because she lost herself that time. While Serena is not that typical , she wants to get away from the upper east side all the time, and her lacking father's love, her weakness, all made chances for Dan to get her. Maybe he can marry Serena, but it can't be the reason to not despise him .
Just as Blair said in the nearly last, he is not one of us, not like Chuck.