4.5 stars! 
 I read this as a bedtime story to my boys (13 and 11) while we waited for the 4th Gregor the Overlander book to arrive at our library. 
 It's told entirely from the point of view of Ivan, a silverback gorilla who's been stuck alone in a cage in a mall for decades, since he was young. Early on, Ivan's voice is fully believeable as a gorilla; he refers to the customers in the mall as "humans foraging" for the "stuff" they need. There were lots of neat little animal-like references early on, though either all of us got used to Ivan and how he spoke, or he really does lose that style of thinking later on in the title. 
 There are also two elephants, a dog, and a few humans involved in the story. Ivan, his plight, and his feelings for his fellow captives touched me. Several times I choked up, and found it difficult to continue reading aloud until I regained my composure. Sure, I cry easily. But not so easy that I don't take note when words can move me that way. Ivan may get under your skin too. 
 The author's note at the end explains how this story is based in part on a real-life gorilla's story, and that made it even more powerful for me. Applegate's word choice, frequent chapter breaks, and penchant for putting lots of space in between lines and paragraphs all entwined to make it a lovely, moving experience. 
 It's fair to tell you that while my boys laughed a few times and they never asked me to stop reading it, at the same time neither of them liked it nearly as much as I did. They deemed it "okay." Even my 11 year old, who is sweet, caring and sensitive (and an animal fan) said that "it just doesn't have enough action in it." This is true, so if you're looking for a rollicking adventure, you may be disappointed. If you're ready to learn about Ivan and his friends, step right up! 
 Edited to add--There are a few nice illustrations throughout the book. Just enough to keep the interest level up. :)