Looking at the synopsis for this series again, I'm actually wondering the exact same thing. Whatever the reason, I am so glad I watched B Gata H Kei, as it was surprisingly one of the best comedy anime series I saw in 2010.
Brace yourself for the synopsis, because, as I mentioned before, it's pretty crazy. The story centers around Yamada, (first name withheld for whatever reason) a high school girl with the face and body of a model. Apon entering high school, Yamada decides on a crazy goal: to have casual sex with 100 boys. However, being self concious of the fact that she is a virgin, she decides she needs to start by targeting a boy who is a virgin as well. She soon crosses paths with Kosuda, the most generic, uninteresting boy she has ever met, who, unfortunately for him, meets Yamada's criteria perfectly.
When watching the first episode of B Gata H Kei, I had incredibly low expectations just from reading the synopsis. Needless to say, I was dead wrong to assume that this series wouldn't be any good. I found myself cracking up several times, sometimes to the point of tears. What makes this series so hillarious is that, as determined as she is, Yamada has no freaking clue what she's doing. She chickens out of her supposedly "brilliant" plans, and when she actually gets the balls to do something, she has no clue where to go next. Admit it: it is so much fun to watch people screw up.
The characters...well they're all idiots. There are several points in the series where you wonder what kind of moron actually does shit like this. Some of the better supporting characters in the series include Tachibana, Yamada's best girl friend who is often rather annoyed with her one-track mind, and Kajenou, a gorgeous American girl with a severe brother complex. But if you've seen this series, you will probably be surprised with my answer. Her name is Misato. She can't really even be considered a supporting character...more like a background character. She is flat chested, short, and generally unnatractive in the eyes of men...which isn't so good considering she likes to follow hot guys around like a lost puppy and drool all over them like a bulldog. Although she only made about one, short appearence per episode, I had to smile every time she appeared.
Flaws? Oh yeah, very many. First of all, like many animes in the comedy-ecchi genre, it fails when it tries to be dramatic. The more sentemental scenes were just boring, and when you watch them, you want them to skip to the comedy as quickly as possible. Second of all, the characters, although very entertaining, were not very well developed. There are several points in the series where the characters do things that, as far as you know, are completely unlike them.
The main problem I had with B Gata H Kei was that if you're going to do a series like this, the comedy has to get better with every episode. With this series, the laugh-chart kind of moved in a straight line, and it got a little bit old after a while.
Overall, I am very glad I gave this series a try. Although I would never say it's the best comedy series I've seen, I can say that it is most likely the best ecchi. I was very sad to see this series come to an end, and I still find myself hoping for more.