The reason why the book could be viewed as negative is because Agassi is really introspective and sensitive. He had huge highs and low lows. For Andre, he stated this in the book, that winning never felt as good as losing did bad. So a lot of the time he spends on talking about things are his disappointments.
I think most tennis players can understand hating tennis and not wanting to play it anymore. Surely I've felt that way after a demoralizing loss, especially against a rival. If you haven't had that feeling that I guess you could understand.
Andre hated tennis because it was forced upon him some best chapters of the book, the earliest chapters detail this. It's very easy to understand why Andre felt the way he did. Also, when he first meets Stephanie in the book. He tells her "his big secret", Andre waits for a shocking response instead she just gives him a look like "doesn't everyone".
Agassi learns to accept his life but I don't think he every really likes tennis until he retires. Up until then, it was his job.
Overall, it was incredibly well written and for the most part each chapter was a nice mix of comedy, sadness, and sometimes triumph. I didn't really like hearing about Agassi's relationships...women or otherwise. Also he withheld a lot of information about his partying, escapades with women, etc. I wouldn't mind reading about some of that stuff. I know he was/is a drinker...he sorta mentions it in the book but I wondered to what extent Andre drank. At one point Gil tells him he'll have to cut back on the alcohol....
Also aside from a handful of matches, Andre didn't really talk about the matches, the points, his strategies. I would have liked to read about this as well. Perhaps he will in another book.
Agassi played some classic matches.