I enjoyed it, but it has some fundamental problems. The cast are engaging. Their banter and interactions are lively. The jokes are funny. However, the premise doesn't make sense and the show fails whenever it tries to build on it. Plus, of course, it's got some of the usual harem problems.
Kiryuu Keiki is an ordinary schoolboy who finds in his locker, one day, an anonymous love letter and a pair of knickers. Provisionally naming this unknown girl "Cinderella", he starts trying to find out who she is. Unfortunately, it turns out that the entire cast is a comedy pervert, despite looking ordinary in ep.1.
This adds interesting spice. It turns out that weird kinky fetishes are good for a romantic comedy. Keiki has a great line in deadpan and a sensible reaction to all these nutters. Unfortunately, things can get problematic. Keiki's best friend and token male sidekick, Shouma Akiyama, is a lolicon. He's only interested in underage girls. Fortunately, he's not a predator and we're only talking about fetishes rather than victims, but some Western viewers might be less amused than the show expects. There's also a sadist girl who wants to enslave Keiki, whom we're supposed to forgive because her emotional connection to him is heartwarming. Uh... well, maybe, but I'd be fleeing at top speed. Ep.10, for instance is a big loud "no, no, absolutely not, ew get away."
Personally speaking, I'd say the show's girls are about fifty-fifty in "yes, I would" and "no, I wouldn't". Since the whole point of the show is to walk that tightrope for comedy, I'd call that a success.
1. We have the inherent problem of harem anime. Since almost the entire female cast is in love with Keiki, albeit in some twisted way or other, it can get increasingly awkward to watch him basically stringing them all along. In fairness, he's giving them clear answers. No, I've repeatedly told you that I'm not your master/owner. No, I don't want to be your slave. Please wear knickers in public. Don't sniff my underwear. Et cetera. Nonetheless, two or three of the girls are extremely serious about him, in their way, while others have clear interest. The harem genre depends on him leaving this situation unresolved, which isn't very nice even if the girls in question tend to express their desires in amusingly questionable ways.
2. It's another show set in that comforting anime world, where boys can just sit around doing nothing and girls will spontaneously fall in love with them. Because they're nice, ahem. Japan then wonders why its otaku reject 3D romance.
3. That love letter is an unconvincing plot device. Keiki spends almost the whole series looking for Cinderella, but he never shows a girl the love letter and asks her if she wrote it. Why not? Even if he'd mentioned the knickers (which wouldn't be necessary), that would be small beer compared with the everyday antics of Sayuki, Yuika and Nanjou. It's hard to imagine anyone batting an eyelid.
4. Then, in the second half, Keiki gets busy investigating a follow-up development. He decides that the panty thief must be Cinderella and then builds yet more inferences upon this questionable premise. (Panty thieves outnumber non-panty thieves in this show... and I'm only counting girls there.)
5. He talks himself into doing some distressing things to Sayuki. It's for comedy, of course, since we know how she'll respond... but, even so, I cringed at the arse-fondling in ep.6 and the skirt-lifting in ep.9.
6. There are some eye-rolling episodes. Ep.11 is just silly. The swimsuits. The love confession competition. The plot requirement for Keiki to have been show-breakingly stupid.
That said, though, the show's funny and nice. When it slows down, it can be lovely. Almost anyone can get the odd charming scene, here and there. It's a good-natured show that likes its cast and doesn't condemn anyone's tastes (although they're understandably a turn-off for Keiki). Its comic timing is strong. Despite the show's speed bumps, I still enjoyed it and would even come close to a recommendation... which is surprisingly strong praise, given its fundamental problems.