To begin with, I advise you to have reached at least episode 1 of season 4 before watching this film because it quickly summarizes all the previous seasons and talks about an event that takes place during episode 1 of season 4. The film was enjoyable; the animation, music, and fight scenes were incredible. However, the story was so predictable that I figured out the twist during the intro. All the characters were underutilized because they were too powerful. I mean, without spoiling anything, just the characters on the poster—Rimuru, Luminous, Hinata, Benimaru, Shion, Soei, Gobta, and Ranga—already had a cast of overpowered characters, and the threatwasn't up to scratch. Again, I'll say it: the film was enjoyable, but nothing more.
It wasn't a bad film, but it wasn't good either. It's entertaining enough, but trying to understand the plot too much gives you a headache because of the plot holes.