Hmmm, I have mixed opinions on the subject.
My personal biggest problem with the Harry Potter world is that it's not especially well defined. Hogwart's is supposed to be the equivilent of say Oxford, Harvard, Yale, or other Ivy league centers of education. All wizards don't attend here, you get an invitation and have to pay tuition which they are very specific about to begin with. There is little, if anything about what everyone else does for education and how they learn magic, which I always found a little distressing, since there seems to be a system of elitism in place where pretty much everyone that matters comes from that one school, irregardless of house.
To be honest I dabble with writing, and even let people read my stuff from time to time. I've actually sat down a few times and tried to write Harry Potter fan fiction addressing that kind of issue... you know, attempts at world expansion other than simply retreading power fantasies based on what's in the books. I typically wind up failing to my own standards though because it's hard for me to deal with the issues I want to, without feeling that I'm getting away from the general style. Typically I wind up trying to write it about an unusually talented, I guess Hermione like mage, who happens to not be rich enough to attend Hogwart's, or a Legacy like the Weaslys (though how poor they actually are is debatable, the father is fairly high up in what amounts to the Secret Service/FBI/CIA all rolled into one, despite attempts to portray it otherwise, George Weasly is NOT by any means a normal guy). This tends get me also thinking along the lines of where Voldemort got all these wizards to follow him, and how the "Order Of The Pheonix" were all pretty much from Hogwarts, there seem to be leaders of the Death Eaters who are unspecified even if a lot of them are from there too. It got me thinking about how many not all Death Eaters are evil per-se, maybe they just by definition hate Hogwarts pretty much running their world with pretty much every leader coming from that school, and it being such an institution they treat attacks on it like someone trying to bomb The White House in the US. Sure Voldemort is evil, but was everyone fighting against the current system?
I could go on about that, but even when I don't even start thinking about potential points of view from the Death Eaters, I start thinking in terms of the decimation of the wizarding world from the war that was just fought, with battles beyond the ones in and around Hogwarts or involving Harry. Less "house" Wizards from Hogwarts, causing wizards from other schools to become more important, probably with resentment... and well... let's just say in the end my overall results before even getting into the plot wind up not being anything like what Dame JK Rowling would write. Even if I put it up on a fan fiction site, I'd expect one of my failed stories (and probably anything I tried to write on the subject) to have fanboys attacking me with torches and pitchforks.
Also the characters I tend to want to play with are ones that aren't all that popular. You know, things like how Mad Eye Moody's eye might have been something similar to a Horcrux he got from someone else, the world's greatest Auror was getting his butt kicked becaue his body was getting old, when he died his soul lived on through the eye and it took a long time but eventually constructed a new, younger body for him. "WTF are you thinking" stuff like that, that largely began with "if this guy is the world's pre-eminant combat mage, how does some goober just bushwhack him and dump him in a trunk? ... hmm well maybe he's part senile in his old age but nobody noticed it... he's just too old".
That said, I always felt that the House system wasn't terrible (though this is very funny). I think the books even said that Slytherin's weren't all evil, it's just we never really dealt with many characters who were from that house that weren't bad guys so the academic point doesn't much matter (well I guess it does, given that from a point of view it can be argued Severus Snape was actually the hero, or if not he was definatly one of the more heroic characters in the end). I've always thought that the houses took some nods from Weis and Hickman's old "Order Of High Sorcery" from Draglonlance, and that the Slytherins were sort of like the Black robes, in the RPGs they are always evil, but in the books and comics it's more ambigious. Dalamar steps up to do the right thing and save the world more than ones, and you had Ladonna and Par Salian involved in a relationship and fighting back to back against bad guys on a couple of occasions in comics and such. Being really ambitious does not mean someone doesn't have their standards. There is a also a differance between "really interested in obtaining more power and prestige" and "willing to stick knives in babies to achieve it". The Hufflepuffs suffer from the "loser" image simply due to nothing being done with them, when actually they seem like potentially the most powerful house because they aren't typecast and there are plenty of very extreme personality types that could get sent there without hitting one of the other bells. I mean we know about Ravenclaw's crown thingy, we know about all the bad guys in Slytherin (and they get focus from being toe to toe with Gryphindor), and of course the main characters are all from Gryphindor house). Pretty much the only detail we know about Hufflepuff is that it was founded by Helga Hufflepuff, as the "everyone not in another catagory" house. If you were going to do a "Potter" sequel it actually seems like the best house perspective to build from, since to me at least it seems like the one house that should keep pwning people by surprise by it's very nature. If I was going to write involving them I'd probably portray them as the guys holding everything together and doing what matters behind the backs of others, because the Ravenclaws are too introspective, and the Slytherins and Gryphindors too arrogant to ever really pay attention to the guys that seem to perpetually be on the losing end of school sporting events, and not totally focused on academics.
Ah well, enough rambling. Good strip. I've ready enough Harry Potter to be something of a fan, and to have put some thought into the universe.