I think it's probably because I was there for it. His construction of the narrative, while better than many (including many straight journalists) ends up sort of falsely casting people into hero/fool/villain roles that make the book work as an entertainment, but don't fully hold up.
It's a decent book, and a decent movie (kudos for one particular scene where I recognized data from the actual LoanPerformance database) I actually prefer the movie Margin Call for more accurately capturing the feel of the crisis from inside a bank.