All right, I will be blunt about this. Chu-Bra!! is a boring title. It is like a kids' slice-of-life with a little ecchi. Oh, and unfunny 'comedy.' There is nothing really mature here, not story- or risque-wise. Yes, do not compare it to the brilliant Kodomo no Jikan.
What we have here is a girl who has just become a middle-schooler, in class 1-A, and it turns out she is obsessed with underwear, which she wants to be happy (yes, I am talking about the underwear). She also wishes to make some friends. After she, Hayama Nayu, does, the steps (chapters) focus on the daily, stand-alone 'adventures' she and two of her classmates have, of course, with an undergarments theme. *Says it in monotone* Get ready to laugh your ass off. It is a good setting for sexy situations, though, so I will give it that.
Believe it or not, this series may actually be more appealing to young girls than any other audience. There are those silly moments when the main character appears passionate about her hobby, and the pathetic attempts at drama, which are sometimes ruined by inappropriate (to the moment) comedy. For boys, the ecchi is not heavy enough to keep them and the story is immature. Along with lasses' mentality, Chu-Bra!! could easily be labelled 'shoujo,' except for the fan-service and better artwork.
Speaking of the art, it is actually the saving grace of the manga. It is neither too detailed nor too simple, just right. The girls look hot, even, except . . .
. . . The characters and their designs are off-putting. I can tell the artist can draw people well, but having the heroine wear glasses and her friends, one looking like an older woman with huge breasts and a somewhat fat body, while the other has the face and chest of nine-year-old and the ass of a fifteen-year-old, was a bad idea. Also, those two, Haruka and Yako-chan, give off supporting-character vibe instead of main ones. (They are similar to Kouda Akari's group in Girl's High, and, in fact, less to Kokonoe Rin's in Kodomo no Jikan. (Come to think of it, Haruka and Yako-chan's ages are between the aforementioned girls in those two series. :P )) There is also Hayama's 'friend,' Seigo-san, a young man who makes underwear she sometimes tests and for some reason lives with her, but he is no Reiji, making him not worth mentioning.
Overall, if you are looking for an average manga to read with no plot-twists (or, hell, a plot) in a lame school-setting, then you may, and I stress 'may,' want to give this a shot. As a a matter of fact, some claim this title is actually educational, giving more incentive to little girls reading it. (Heh, little girls watching little girls get naked; that would be fun to see.) In case you are not one, however, I would recommend the titles I mentioned above (the anime version in case of Girl's High), as they have analogical settings and characters with better execution.