Let's take a look at exactly what Opus Dei says they are, and what their critics and former members claim they are. Opus Dei says that they're essentially an organization that provides guidelines on how Christian laypeople can live "a life fully consistent with their faith, in the middle of ordinary circumstances of their lives." That involves things like "divine filiation," embracing Christian values like "charity, patience, humility, diligence, integrity, [and] cheerfulness," prayer, the offering of sacrifices, and "sanctifying work," which means work that's done "ethically."
That sounds not-so-bad, but like anything involving people, it gets very complicated very quickly. Opus Dei has claimed to be different things over the years: NPR says it's currently defined as a "personal prelature," but it's also been called things like a "secular institute" and a "priestly society of common life without vows." Both laypeople and clergy are members, new members are usually recruited by existing members, and when joining Opus Dei, a contract is signed promising (in part): "with firm resolve I dedicate myself to pursue sanctity and to practice apostolate with all my energy."
Critics, however, accuse Opus Dei of being everything up to and including a right-wing cult. Take, for example, a joke published in the magazine Tablet: "How many members of Opus Dei does it take to screw in a lightbulb? The answer is, 100... one to screw in the lightbulb, and 99 to chant, 'We are not a movement, we are not a movement.'"
