Very interesting question. I guess I have my own ideas of what I think are key characteristics of each house. I guess I'll just post them as a starting point, even if some of them are perhaps more commonly known things:
Slytherin: Not just cunning and ambitious, but I see them as generally more self centered and motivated by self gain. I am not saying that's necessarily an evil thing, but I just think that's how their minds work. I don't see them as necessarily being a house that loves to come together for teamwork--not unless there is a common "treasure* of some sort that they all will get some gain from--i.e, a goal of winning the house cup because of what it means to them, or working together on a prank for the joy of seeing someone else inconvenienced. I do see them being strongly steeped in tradition. Some of the Slytherins come from long lines of family members who have belonged to the house and therefore they have a very strong, aggressive sense of house pride and it seems to shape their code of ethics and values. I think a lot of the Slytherins have been, more or less, shoved out into the world by their self centered parents and have learned they needed to be self centered as well or their own needs did not get met. ie, Draco Malfoy as a prime example.
Gryffindor: In many respects I see Gryfffys as being the polar opposite of Slytherins. A Gryffy values teamwork, love, honesty, family and friends far more than their own individual accomplishments. They love teamwork and the sense of loyalty, friendship and family that teamwork gives them. A Gryffy not only will resist throwing someone under the bus as much as possible, but they would be the first to jump, themselves, under the bus in order to protect someone else. I don't see a Slytherin really ever doing that, quite honestly. Gryffys seem to always be looking at the greater good and concentrating on moving towards that goal as a pack, even if it means they must use themselves as pawns in some manner to accomplish that end. Gryffindors are very strongwilled, generous, honest sometimes to their own detriment, ambitious, intelligent but not necessarily in a devious way. Their strong will and determination to always be looking to thwart the dark arts helps them bond and also helps them learn that being cohesive is a marvelous weapon as well as a support. Gryffs tend to have long lines of generational succession as well, but I think its because they are raised in families who have strong bonds and connections and teach their children to treasure those same values. It forms that desire for a Gryff to connect not only to the present, but the past and the future. Example: Remus Lupin, Harry Potter, Albus Dumbeldore.
Ravenclaws: I guess I see Ravenclaws being the bunch that is perhaps a bit more streetwise. I see them as being tenacious, fun loving, good spirited, and energetic. I guess when I think of a Ravenclaw, I see someone who is perhaps a goodhearted, streetwise student who is not above pranks for the fun of it--not in a meanspirited way, but just for fun. I see them as being, for the most part, quick tempered, but their tempers not being longlasting, and I think they are sort of a midground between gryffindor and slytherin. I see them having the cunning that a slytherin has but the goodheartedness, for the most part, of a gryffindor, but with a dash more of an independent spirit thrown in. I think a class clown might be more apt to come from here, if it is relatively harmless fun that is at work. Examples: Luna Lovegood, Moaning Myrtle.
Hufflepuff--I see these students as being different from what is sort of assumed. When I see a Hufflepuff, I see someone who is very individualistic, not afraid to be independent, knowing full well the difference between being alone and being lonely. I see them as being perhaps some of the hardest working and most dedicated of any of the houses. I think once a Hufflepuff sets into doing a task, I believe they will work at it methodically and painstakingly, and in a dedicated fashion until they accomplish what they set out to do. I see them as perhaps more deeply intellectual, not needing to be the life of the party in order to be satisfied with themselves and their lives but being secure in who they themselves are. I see the "loners" or outcasts as being placed in Hufflepuff because many of them do have a certain contentedness in being an individual. And because they all are so alike in their personalities, I think it allows them to come together when necessary, as a house for team events. Example: Nymphadora Tonks, Professor Sprout.
How'd I do?
K.