My dad once said to me, "You give a lot of books three stars." I do.
Some light spoilers follow.
Interesting concept bogged down by too many characters and too many storylines.
Choldenko (I thought this author's name was Cholden for the longest time because our spine labels only carry the first 7 of an author's surname) was unconvincing writing as a boy. I think the book suffers from being limited to Moose's perspective alone. I didn't really understand his relationship with his mother until his father spells it out at one point. And what as the deal with Piper? I felt like I was getting whiplash trying to figure out if Moose liked her or not (and ultimately it's a moot point, so why include it at all? He seemed to like Scout about the same as Piper and I preferred that relationship).
The historical fiction aspect was also a big miss for me. I only really knew it was the 1930s because the book kept telling me and because they were living on Alcatraz.
Almost every aspect seems to exist to service the plot, which was too fractured for me to really get into it. I wish the story were more streamlined, characters were better developed, and the conflicts made more explicit. One of the main conflicts is so vague I think that made it more sinister than Choldenko intended. However, I also think this is something only adults would worry about and that the lack of details will be fine for kids reading the books (they'll either pick up on it or they won't).
I will admit to getting chills at the ending. I really bought into the mythos of Al Capone on Alcatraz. That aspect of the book was effective. But that part of the book is gone so quickly and then the whole thing is over, it's hard to say that it felt that satisfying. I'd be interested to see where the sequels go, but I'll probably just Google the books rather than reading them.
ETA: There is a scene at the end of the book between Moose and the warden that I did really like. Moose thinks how the warden tells him that Moose is almost a man and needs to act like it, but the warden treats Moose like a child. That to me is the 12-year-old feeling. That weird transitional period of life. I wanted more of that.