I'm not going to bother delving into the blatant historical and mythological errors of this movie.
First off, the only pentacles in the movie were used by the bad guys (Morganians, after the sorceress Morgan la Fey), perpetuating the lie that they are associated with evil. And the tools used were considered vital for practicing magic, despite the fact that, that is not true in real life. Only an insecure young man is able to overcome this obstacle, despite his elders having practiced for hundreds of years. Once again, Hollywood emphasizes youth over wisdom and experience.
Then there's the centuries old dichotomy of male wizards good/female witches bad. The most powerful female sorceress is automatically evil, and the most powerful male conjurors are good (Merlinians, after Merlyn). Despite the fact that Morgaine was originally a healer, actually treating Arthur when he went to Avalon, seriously wounded. It wasn't until later cycles when she was portrayed as being evil and conniving, likely because she did not adhere to the sexual ethics projected onto women of that time period. In other words, since she was not a virgin and refused to settle into an arranged marriage, she had to be a whore and therefore demonized for it.
The movie fails the Bechdel Test, obviously. The female characters are either in need of rescuing, rewards for a job well done, or evil and need to be defeated. When Dave tries to keep Becky safe, she tells Dave that she is already involved and might as well help save the world. Dave, the physics geek, says that, that's sexy. I wanted to throttle the character because he's wanting to treat her like the reward he sees her as by keeping her on the pedestal he's placed her on for so many years: safe and pristine. He's supposed to be a geek and is just NOW figuring out that intelligence is a turn-on? I'm not even touching the resurgence of emo boys stalking the women whom they allegedly love. Some things from the '80's should have been left there.
If you're the kind of person that can turn your brain off, it's an enjoyable flick. If you're like me and unable to dissociate entertainment from larger sociological problems, you might find your blood pressure rising to unsafe levels.