It's not just one pure evil guy (or woman) versus the heroes. (businessinsider.com)
Directors Anthony and Joe Russo have at least four plot threads going at once, all headed in the same direction — evil guy Thanos (Josh Brolin, purportedly) wants the stones because when they are affixed to his magical gauntlet, he will acquire unlimited power to wage a campaign of extermination across the universe. (philly.com)