Bartholomew Bogue, the evil mine owner (played by Peter Sarsgaard doing a passable John Malkovich impersonation), has been terrorizing the nearby town of Rose Creek. The town folk are represented as a bunch of simple farmers, although there is not a sign of crops anywhere. I'd think that in real life, Rose Creek would be a rough and tumble mining town filled with saloons, gambling establishments and prostitutes. For reasons that are not clear, Bogue wants to buy the town and offers the town folks a deal: pay me a pittance for the land and leave, or I'll kill you all. To impress the folks that he's serious, he burns down the church and gratuitously kills a few guys.
The first half or so of the movie was the best. Emma Cullen (Halley Bennett), whose husband was killed by Bogue, takes it upon herself to buy some protection. She meets up with lawman Sam Chisolm (Denzel Washington) and he agrees to recruit a team to help her for whatever it was in the black bag she was carrying. Chisolm recruits a racially diverse group of seven gunman, gamblers, an Indian, and Civil War veterans (one of which seems to suffering from PTSD). As Josh Faraday (Chris Pratt) says during the process "Oh good, we got us a Mexican".
Chisolm and his recruits set about trying to train the townsfolk into something approximating a militia. They look pretty hopeless. Bogue and his men are out of town for 3 weeks giving the seven ample time to plan a defense of the town, making liberal use of the mine's dynamite and weapons.
What follows is a bloody slaughter. Between rifle and hand gun shootings, explosions, stabbings, arrows and a Gatling gun, I would estimate that 350 people get killed, mostly Bogue's hired men.
The magnificent seven guys are mostly presented as good guys, willing to die for a good cause, so you don't feel bad about cheering for them to win. It also turns out that Chisolm has reasons of his own for joining the fray.
One thing I learned from researching for this review is that the 1960 version (according to Wikipedia) is the 2nd most seen movie on TV, after "The Wizard of Oz".