I haven't gone into full detail as to why I love the Melancholy of Haruhi Suzumiya so much. In my review, I said that it, "Makes fun of everything I hate in anime." Well, allow me to get in depth.
In the anime and manga markets, most franchises are one of two things: shonen action series, a la Dragonball, Naruto, Bleach, et cetera, or high school comedies. Almost every comedic anime and/or manga series I know of is in a high school setting: School Rumble, Azumanga Dai-Oh, Lucky Star, you name it. HS is no different. However, it not only spoofs the high school comedies, but many other aspects of J-pop culture as well.
I was never disturbed by the sexual fanservice in HS, because the show brilliantly illustrated how ridiculous such fanservice is in most anime. In any typical series, the cute and/or sexy girls will be wearing revealing outfits and/or fetish costumes for no plausible reason at all within the universe. In HS, Haruhi, trying to turn Mikuru into a sex symbol, always forces her into costumes against her will. Sure, the gag gets old after a while, but it's satiring how authors often treat their characters; not as real people, but rather, as toy dolls. Of course, HS does this only for humorous effect, but most anime series don't get me writing intellectually like this, either.
Another thing is, there's a character for everyone. There is Kyon, the sarcastic male lead who is wise beyond his years. There is Haruhi, the female lead who is wildly eccentric, yet conceals a complex personality. There is Yuki, a stereotypical silent girl, (think Wonder Doll, but even more emotionless.) but who is revealed to actually be a very caring individual, despite her lack of social graces. There is Mikuru, who appears to be a "moe" girl at first glance, but the episode which reveals her "older" self shows that she wasn't always an emotionally frail child. There is Itsuki, whom no one can really tell what he is thinking, yet is at the beck and call of an "Organization" only he knows about. There's Taniguchi, a self-proclaimed ladies' man who is really just a girl crazy freak, Tsuruya, a silly high school girl who sometimes goes along with Haruhi's schemes just because she thinks they're hilarious, Ryoko, a sweet girl with a pretty voice who, like many of the other characters, is concealing something, the Computer Club President, who is a stereotypical nerd ratched up to "11", Kyon's Sister, who seems to be thrown in just for fun, among others. Everyone comes to love at least one character. For me, it's Kyon. For others, it may or may not be someone else. Characterization was not skimped over, even for the characters rife with anime cliches.
And, well, it's just different. What if you went to high school, and almost all of the students were not really students? You'd be in Kyon's position. But who, in history, has ever been in Kyon's position? Especially when you take his sarcastic mannerisms into account? Exactly. Kyon is far more mature than most other high school students, almost like he is an adult re-living high school. Haruhi is almost schizophrenic in how one moment, she laments how insignificant the people who attend a baseball game are, sounding like Eeyore in doing so, and the next moment, will stop an nothing to win a strategy PC game, all while displaying the bombast of a 12-year old in the depths of a sugar high. Yuki, Mikuru, and Itsuki are deconstructions of what have become tired cliches in J-pop culture. And, well, it's just funny! And you actually end up caring for the characters, oddly enough.
And if that still doesn't sway you, then there's this: the baseball game in episode 7 remains one of the funniest things I've ever seen on a tv show. This is the only foreign-made tv show I know of that can make me laugh like my favorite American-made sitcoms.
So there. Believe the hype. Take up Haruhi-ism or suffer the penalty!