The Western, which stars Jamie Foxx and Leonardo DiCaprio, is set in slavery-era Mississippi in 1858 and has sparked debate over repeated use of racial slurs.
The X Factor judge insists he enjoyed the film, but felt Tarantino should have been more been more careful when addressing such a "painful part of American history".
He tells New York Post gossip column Page Six, "Django Unchained is a powerful story and incredibly entertaining movie. The performances are all stellar, particularly Leo DiCaprio's and Samuel L. Jackson's. Jamie Foxx was also very strong.
"One criticism: Although the N-word was unfortunately used liberally during the time the film depicted, I felt Q.T. (Quentin Tarantino) should have approached the use of the word more sensitively and used it a lot less... It's a painful part of America's history and still an open wound."
Reid is not alone in his criticism - director Spike Lee recently vowed never to watch Tarantino's latest offering because of the controversial language and themes.