The Overarching message (of the HP books)

[potions_mistress_13]

No: HPFGUIDX 191681

Potioncat:
I do agree that every set of House Attributes has a set of vices. Gryffindor courage becomes recklessness; Ravenclaw wit becomes learning for its own sake, a detachment; Hufflepuff loyalty becomes blind obedience; Slytherin ambition becomes a drive to prove oneself. (Oops, the last one was a vice turned attribute.)

Elena:
Beyond the drive to prove oneself (a positive), I suggest that Slytherin's downside is as follows: ambition becomes a ruthless drive to do anything necessary to better oneself. 

Potioncat:
It seems to me that JKR has ranked the attributes into Gryffindor, Hufflepuff, Ravenclaw and a trailing Slytherin.

Elena:
There can be little doubt that JKR ranked Gryffindor first, and Slytherin last. I am not so sure about the middle two houses. JKR does not clearly rank Hufflepuff and Ravenclaw in comparison to each other. Cedric is a Hufflepuff, while Luna belongs to Ravenclaw house. Both are central, positive figures. Members of the DA come from both houses, and only a moment separates the two houses rising in support of Harry just before the battle of Hogwarts.