Just read the first volume and chapters 9, 10, and 11: excellent. The plot is, as you can tell from the description, about children who have raised in a controlled environment by bad people. However, the story consists of far more than just the exploitation of an idea. It's exciting yet down-to-earth. The storyline and characters' reactions are all very realistic. There's no epic "one-liners", this isn't a story which is there to entertain, it's not action-packed either. It's just an extremely engaging plot, with well-paced introduction of plot elements. If you've read Battle Royale, then this comparison will be useful: just as in Battle Royale, in The Hour of the Mice you come to care deeply about the characters and their struggles, to the extent that once you finish all the chapters you'll be feeling anxious for the characters and want to read more.
With a lame title like "The Hour of the Mice" I didn't expect a lot, but I was happily surprised. For instance, I feared the pacing would be full of quick plot developments consisting mainly of the characters running around or having constant close calls, but it's not rushed at all, and every development flows naturally. Also, there are other plot threads starting to weave themselves in near the beginning of the third volume, so it seems like this story could have epic potential. It's starting to give me a little bit of the feel of Highschool of the Dead, by the way (in semblance--it's much better, unless "less fanservice" = "worse" for you).
My only complaint is that it's 25-page monthly chapters, with only 3 volumes since 2004. ;_; It's totally believable: there's no part of this story or behavior of an individual person or character which I couldn't possibly see happen IRL in fact, to my amazement. The pace isn't very quick yet they've revealed a surprising amount of information: we're presented with the general idea of events that occur in the story, although obviously we don't have a totally clear idea about the exact nature of situations, and the characters have developed a lot in just the first volume, so it's far from unyielding. And it's only inconsequential to the extent that you don't care about the characters (humans being experimented upon without their knowing isn't "new", obviously, but the plot is well-constructed). That's my personal opinion. By the way, the art grows on you.