Back in January, Sundance went gaga over The Birth of a Nation, a historical epic based on Nat Turner's 1831 slave rebellion, co-written, co-produced and directed by Nate Parker. Fox Searchlight Pictures pounced, buying the worldwide rights to the film in an unprecedented $17.5 million deal.

Here was an exciting new African-American auteur; here was the remedy to the ongoing #oscarssowhite rumblings; here was a film that was prepared to stand toe-to-toe with DW Griffith’s identically titled 1915 paean to the Ku Klux Klan.

Then last summer, a more chilling narrative emerged. In 1999, as a student and wrestler at Penn State University, Parker and his roommate Jean Celestin – his co-writer on The Birth of a Nation – were charged with raping a 18-year-old female student.

Parker was acquitted in a 2001 trial, but Celestin was not. The ugly details and fallout – harassment, an out-of-court settlement, the subsequent suicide of the victim – have been poured over for months.

It’s an awful, inappropriate introduction to a flawed, decently entertaining biopic. Parker’s rather-too-soft Nat Turner (also played by Parker) grows up on a Virginia plantation and is taught to read by his more-humane-than-most subjugators. When he isn’t toiling in the fields, he preaches Bible, a skill soon exploited by his ‘master’, Samuel Turner (an impressive Armie Hammer) and other slave-owners willing to pay for a black preacher to quell possible discontents among their own slaves.

There are clever observations about the use of religion as an oppressive instrument and how slave-owning, perhaps even more than slavitude, erodes personhood. In this spirit, Samuel is not as sadistic as many of the owners that Nat encounters, but his humanity only makes his ownership all the more monstrous.

There are also misjudged and some downright cornball moments: a final shot reaches for legacy and finds hellish movie cliché, Nat’s “acquisition” of his wife (Aja Naomi King) is queasy, and the moment when he “invents” evangelical-style preaching is downright silly.

If it were an episode of the recently rebooted (and warmly recommended) Roots, we'd have no complaints. But if you're attempting a riposte of Griffith's unfortunately themed masterpiece (a film that created much of our common cinematic grammar) then you better have something audacious to show us.

Sadly, The Birth of a Nation is not nearly as innovative as 12 Years a Slave or Django Unchained. Save for a few vaguely psychedelic dream sequences that seem to hark back to the trippier moments of Sweet Sweetback's Baadasssss Song, this is a square, conventional portrait, not befitting of a revolution or a revolutionary.