It's a successful but often insubstantial comedy. There are some weaker episodes in the middle, but I liked the finale and the show's closing stretch is making laudable efforts to turn the main cast into human beings. Firstly, though...
Parody! It's parody, everyone. It's exaggerating shoujo manga cliches and having such fun that it's funny to anyone, which is both the show's blessing and its curse. It's taking all the fangirl-pleasing stereotypes and pushing them to breaking point for comedy value. The Host Club is a place where beautiful boys entertain girls with way too much free time, play-acting like crazy to make their customers squee. (This is a lot more innocent than real host clubs, incidentally.) The club's hosts are all shoujo fantasy types and include:
(a) Tamaki, the club president and a deranged narcissistic loon who overreacts to everything and lives only to make the world happy. In the presence of customers, he becomes the embodiment of every romantic cliche, delivering dialogue so purple that there ought to be a law against it. Imagine the heart-bursting climax of a Mills and Boon. Tamaki's like that all the time.
(b/c) Hikaru and Kaoru, the twins. Their schtick involves pretending to be delicate wounded flowers who exist only to comfort each other's wounded souls. Preferably naked. With kisses. In reality, though, they're immature and often unpleasant.
(d) Kyoya, the Cool, Calculating One.
(e) Honey, the "shota" character, i.e. the gender-flipped equivalent of a lolita complex. He's actually the oldest member of the club, but he looks like a ten-year-old and is always eating sweets.
(f) Mori, the Strong And Silent One. He's effectively Honey's bodyguard, which is ironic since as it happens cute little Honey is one of the most feared martial artists on the planet and in danger of being called a Weapon of Mass Destruction.
For what it's worth, Tomoko felt that this wasn't enough boys. She'd have included a muscle-bound idiot, plus ideally also a teacher and some comic relief with an Osaka accent. This show pays remarkably little attention to its school setting, curiously. No teachers. No change to the school uniforms in summer. Precious few school events. This might be because Ouran High School is for the insanely rich and powerful, so probably offers a good deal of wriggle room with homework and exams. If you're smart and keen to study, you'll get a world-beating education. However if you're as thick as two short planks, the evidence suggests that you won't be short of company. One of the show's best running gags is our heroes' obliviousness to real life, which to them means "commoners". Instant coffee, for instance.
Fortunately, there's a drop of vinegar in the syrup. Our hero(ine) is Haruhi, a girl from a poor family who won a place at Ouran on a scholarship. She thinks (rightly) that these people are idiots. She has no interest in shoujo fantasies, host clubs or indeed femininity. She dresses like a boy. However on breaking a vase in episode one and accruing a debt she couldn't pay off in a hundred years, she finds herself being inducted into the Host Club as their latest member, to call her new friends morons and pass sardonic comment on their antics.
The good news: Haruhi's great. She's the voice of sanity. She's immune to squealing nonsense and she treats everyone on their merits. (Ouch.) She's not the cuddliest of characters, but she's at the heart of the show and the simple fact of her presence will eventually start to pop a few bubbles and help her new friends, a little, to grow up. I also liked the way she brought a little real life into the series, e.g. her summer job, or her widowed father. (He's also a drag queen, but that's not important.)
The bad news, though, is that for a good two-thirds of the show, there's almost no weight or significance to the characters. They just goof around, spoofing shoujo cliches and loving themselves. Sometimes this is funny. I loved the Takarazuka episodes (ep.9, ep.19), which are at once scary and accurate. Takarazuka fandom, yow. However the main characters aren't dramatic, because they're very happy with the way things are and they don't want for anything. Eventually we discover that that's not true... but only for half of them. Honey, Mori and even arguably Haruhi herself are basically stable and know exactly what they're doing. They're fine and they have interesting backstory, but dramatically they're static. Admittedly there's unresolved sexual tension between Haruhi and certain of her fellow hosts (to which all parties are oblivious), but surprisingly this never goes anywhere. This show is a parody of romantic shoujo cliches that's deliberately avoiding romance.
Personally, I think the reason is because the show's about families. Of course it's basically candyfloss and it would be silly to claim it's being particularly serious about anything, but it has a heart and I think families are pretty close to it. Haruhi and Tamaki both have no siblings and have lost their mothers. None of the rich kids have a normal, healthy home life, with families that will be some combination of missing, distant, dictatorial or evil. They're liable to be treated as subordinates, not children. This makes sense of the utter lack of romance in the Host Club, despite the fact that it's dripping with play-acted romantic cliches. Tamaki founded it as a way to build a family. He seems to fall in love with Haruhi almost immediately, but his way of expressing this involves calling himself her father. That's one of a few things here that felt odd until I'd thought things through, but the show's actually very clear about this family metaphor.
This is shown most strongly in the ending. Tamaki's family are vile and Kyoya's aren't much better. That grandmother is evil. They nearly destroy the Host Club and then go unpunished when their plan fails... but look at the two fathers' last scene together. After coming to some kind of resolution, they then show that they've learned nothing by starting to argue about who gets to choose Haruhi for a daughter-in-law. It hasn't occurred to either of them that there could be things beyond their control and that Haruhi might have opinions of her own.
I liked that ending a lot. It gives the show emotional weight that, until then, it had lacked. I'd have been happier still had they done more, earlier, with its revelations, but to say that is to wish that I'd been watching a different show. This is essentially a silly comedy and that strong two-part finale is a grafted-on conclusion that comes from the anime producers, not the original manga.
For what it's worth, the characters who do attain some dramatic depth are Tamaki (the show's deranged dynamo), the deeply repressed Kyoya and the spectacularly broken twins. The latter are sadistic emotional cripples and conflicted even about whether they want to get over that. There's a lot of potential pain under the surface of these people, but we almost never glimpse it under their frivolous, pampered lives.
No, I tell a lie. There's a yakuza thug in ep.22-23 who's got more fire than everyone else in the show put together. He's funny, but he's another example of the show only starting to fix itself in the closing stretch.
Cool observation for anyone who's watched the last two episodes... Eclair Tonnerre's name translated into English means lightning and thunder, which are the only two things that scare Haruhi.
Do I like this show? Yes, I think so. It ended well and I laughed quite often along the way. Tomoko was more lukewarm about it, though, and I can see her point. It tends to lack dramatic weight. It's fun, but throwaway. I could also have lived without the likes of Honey's toothache (ep.12) or the Alice in Wonderland episode (ep.13). Nonetheless I have some affection for the characters, while at its best this is a pretty good comedy. I'm also a little curious about the 2011 live-action adaptation. There are significant things here that I'd have done differently, but I can understand why the show became so popular and I'm glad I watched it.