Spoilers ahead....
First of all, stories written in first-person are too easily done wrong. It takes a special writer to make a very compelling story with lots of characters in first-person. It's hard to develop characters because the main character is in every scene and everything has to revolve around him/her. Water for Elephants fell victim to this right from the start.
It moved too fast as well. One minute he's in school and then just like that, his parents die and he's running off and randomly jumps a train that just happens to be a circus train. That's fine, but all that from the beginning could have been scrapped and had him explaining all of the factors that led to him to end up with the circus through interaction with another character. You know, a scene where he's opening up to someone (most likely the Marlena character) and telling his past. Either that or spend more that a few dozen pages on his life before the circus.
I would have liked it if he had "paid his dues" so to speak a little more before ascending to his higher position. Maybe more of an intense scene where he heals some animal or does it secretly or something. Not just diagnosing one of the horses as terminal and then poof!, you're in the good graces of the higher-ups. I wasn't convinced that he had done enough to earn August's trust and become that close to him. And what was with that scene when August introduced him to Uncle Al when Al went apeshit and smashed the glass cup on the floor? That was stupid and made no sense.
I also wasn't sold on Jacob's intense hatred towards August. Ok, August beat the elephant and wouldn't let him give the other animals water until after Al had made a deal. Animal cruelty has to be expected when talking about the circus in the 30s. Hell, animals in zoos in this day and age are treated poorly, let alone some second-rate circus eighty years ago. But trying to portray August as some kind of monster was a failure on the author's part. Sure, he might have been a jerk I guess and was rude to the people in the diner, but someone who deserved to die? And this was all before he hit Marlena. Sure, that's despicable, but let's remember the context here: this is the 1930s, women had only been allowed to vote for a handful of years and were still seen and regarded as baby-factories for the most part. Him hitting her (once, not every night or anything like that) didn't seem to warrant his portrayal of some vicious, evil person. A worthless asshole, sure. If he really was supposed to be a schizophrenic, then that was also a failure on the author's part. A laughable failure at that.
The romance between Jacob and Marlena was contrived and not genuine. There weren't enough instances where you could feel and sense the attraction growing between them. The idea I guess was to paint a picture of some evil, wife-beating and animal-beating monster who doesn't deserve his lovely innocent wife so the young, newcomer has to save her from him.
Camel and Walter getting thrown from the train was... eh whatever. I didn't care at that point. I just wanted the book to be over.
As for the chapters of Jacob as an old man in the nursing home... those were the only bright spots in the book, but for being 93 years old, he was quite alert and lucid in his speech I thought. The end... gah, give me a break. Yeah, some manager of a circus just happens to know of "one of the greatest circus disasters in history." How convenient. And he agrees to let Jacob stay with the circus knowing that he escaped from the nursing home and people are looking for him? He's 93. He needs constant assistance and near 24 hour care not to mention who knows how much medication. Sure, you can stay! No problem! Alrighty.