It's a very good movie.
For the most part, I really like movies that tell about journalists uncovering stories (i.e., Killing Fields, The Insider, Frost/Nixon, etc.). I sort of romanticize these stories. In another life, I would love to be an "investigatory" journalist.
Michael Keaton is one of my favorite actors. I have really come around to like Mark Ruffalo. I used to loathe him as an actor but now appreciate his work after seeing We Don't Live Here Anymore, Foxcatcher, and now Spotlight. I also really liked Liev Schreiber in this movie.
On the topic of rated R movies, this movie emphasizes to me that my stand on the issue is correct. I will never let the MPAA tell me categorically what I should and should not see. Spotlight is rated R because it has seven F words, some other minor swearing, but mostly because the subject matter is intense (child sexual abuse). There is no sex or nudity in the movie, and it only talks about child abuse in moderately candid terms.
This is a movie worth seeing.