Q:

How accurate is American Crime Story: OJ Simpson?

Beware of minor spoilers if you know nothing about the OJ Simpson story.
How accurate is the series American Crime Story: People V OJ Simpson? All the trials/hearings were televised (according to the series, if I'm not mistaken), and I'm guessing most of the facts are now public as well, since almost all major players wrote books about it.
Is the actual story known (do books agree on the same version of meetings and discussions), and is the series true to its story? Or is there a lot of creative liberty from the directors and writers? Do the hearings follow the original script and the defense made by the Dream Team and the offense?

A:

Expecting an exact match between real life events and the series is never going to happen, because not everyone will agree to the same version of events (e.g. backroom meetings, etc.). Jeffrey Toobin, who wrote The Run of His Life, was a consultant on the series and told the following to E! News:

"This series is not a documentary," Toobin, who's a consultant on the
  series, has explained. "It is not a word-for-word recreation. But in
  terms of the essential truths of the events, in terms of the insights
  into the characters, it is brilliant and everyone will learn a lot and
  be entertained a lot."

This article then goes on to attempt to separate fact from fiction, e.g.:

FACT, for the most part. Robert recalled to Barbara Walters in 1996
  confronting O.J., who was looking at pictures of his children and had
  a gun wrapped in a towel. "In the book it says you said to him,' You
  can't kill yourself, this is my daughter's room,'" Walters recalled a
  line from the 1996 book American Tragedy: The Uncensored Story of the
  Simpson Defense. "I said," Kardashian concurred, "'O.J., I could never
  walk in this room. My daughter couldn't sleep in this bed, she'd know
  what happened here.'"

But it also points out:

Nitpicks: 

Kardashian, who's being painted as the voice of reason, wasn't the one to tell O.J. he needed a more hardcore defense attorney and call
  Robert Shapiro, who's lunching at Mr. Chow when he gets the call in
  the show. In reality, TV exec Roger King stepped in and called
  Shapiro, who was actually at House of Blues.
Marcia Clark had to cancel going to a bridal shower she was throwing, she didn't forget about a friend's baby shower. (It's far bitchier to
  forget about a baby shower, though.)
There's video of young Kim and Kourtney Kardashian at Nicole's funeral in real life, but who's to say whether Kris had to scold Khloe
  and Kourtney for horsing around, telling them to put away the candy,
  as she does in the show? Hmmm…

It's a long article and there's far too much to reprise here.

A:

Generally it's very accurate, mostly because the writers Scott Alexander and Larry Karaszewski had tons of material to work on:

Due to the high-profile nature of the trial, not only did the
  production have copious amounts of video footage and media coverage as
  a base but also most of the main players wrote their own books about
  the experience. “I think we’re very proud to how close we stayed to
  the truth while creating drama out of recent history,” says Alexander. 
Vulture's review of the season praises American Crime Story's
  historical accuracy, saying that "devotees of Toobin’s book will be
  struck by how much inspiration this series takes from his reporting,
  as well as its overall affinity for sticking to what actually happened
  rather than embellishing or inventing details — though admittedly,
  with a case this notorious, what would be the point of making stuff
  up?" (source)

As mentioned above the show main inspiration was Jeffrey Toobin's book The Run Of His Life: The People v. O.J. Simpson, so in cases where there is no general agreement on the actual events the writers were probably sticking to the book version. Note that the book itself is seen as professional and objective:

The New York Times review extolled the non-fiction work as "a
  comprehensive, professional account, unburdened by the
  self-justifications of parties to the case." (source)

That said, there have been some liberalisations of the facts, simply because the story had to be told as a TV series:

Due to time constraints of the 10-hour miniseries, there have been
  some aspects that were altered. Adds executive producer Brad Simpson
  (World War Z), “If we’re gonna get dinged, it’s because we have to
  consolidate things. It’s a dramatic retelling. We’ve consolidated
  time. We’ve consolidated characters. But in terms of the truth of what
  happened, I feel like we’ve been really honest.”
  (source)

For what it's worth Marcia Clark has a very good opinion of the series.

