Selma isn't exactly a biopic, which is made evident by the title, which is not King. It's a representation of a historical moment, with many famous participants, of whom Dr. Martin Luther King, Jr. sits at the top. But King is shown as a leader amongst equals.
DuVernay effectively tells the story of the Selma to Montgomery march, without moving too far from the actual events. The drama doesn't need much tarting up ... it remains both shocking and inspiring. David Oyelowo makes a memorable King (he is one of several actors from England in key parts ... you don't notice it). Some have questioned the representation of the relationship between King and Lyndon Johnson. I don't think it's a huge flaw, but at times it feels like DuVernay is using LBJ as a plot device to add tension. The film rights to King's actual speeches had already been licensed, so DuVernay wrote versions of those speeches. It works for the most part, although when King is giving a speech you might know by heart, it's a bit jarring.
Selma was nominated for a Best Picture Oscar (it also won Best Song). I've seen all but one of the nominees, and I think Selma is better than the winner, Birdman or (The Unexpected Virtue of Ignorance). I might have voted for Boyhood, but Selma definitely belonged in the discussion. The absence of DuVernay in the nominations for Best Director and Best Screenplay, along with David Oyelowo being ignored for Best Actor, pointed to the lack of diversity among the Academy voters.
Selma is solid, raised by some fine acting and a good script. I'm sorry it took me this long to finally see it. #590 on the They Shoot Pictures, Don't They list of the top 1000 films of the 21st century.