As someone mentioned, the development between Himuro and Ayaki is probably the most interesting thing in this manga. It's the reason why I suffered through Fukada Kyoko's atrocious acting in the drama version, and it's why I read all 10 volumes in 2 days.
Some of the cases were pretty weak and the "evidence" is flimsy - it seems we're expected to simply accept what we're told as truth, at times, with the only reason being "Himuro is a genius and therefore he is always right." That said, they have entertainment value, and not all the cases fell flat. Some had pretty interesting twists, and it took a bit of pondering to figure out who actually did it. Others... well, you could see the ending coming a mile away, but it's still somewhat interesting to see how the characters handled it and reacted to it.
As the centre of the series, Himuro wasn't really given too much depth or real screentime. We know he's had a dark past, that it has something to do with his inability to move out of the room, but for the most part, we're barely allowed to know him. Ayaki comes across as surprisingly idiotic for someone who's supposed to be "smart, with guts and guile", but she's bearable, and the author did well to develop her character as the series wore on. She was noticeably smarter and more spontaneous than she was at the beginning, and definitely less reliant on Himuro.
Now, the art. Absolutely terrible. The very first shot of Ayaki in the first chapter shocked me beyond words. The characters are all blocky outlines filled with splotches of grey at a failed attempt at shadowing, proportions are wrong, and at various points, facial features are completely unaligned. If you're anal about art, I suggest you run as far as you can.
Overall, this manga wasn't quite as bad as it sounds. If you can bear with the art (and it gets slightly better, though I still got occasional urges to poke my eyes out), unnecessary fanservice, and read it without being overly critical, it's reasonably entertaining. Fans of the mystery/detective genre might enjoy the cases, if nothing else.