An 8 out of 10.
before Odo and the various shape changing lifeforms found throughout Trek there was Star Trek's
Salt Vampire. TOS took the hoary old story of the alien monster killing everyone and turns it on its head. They make an effort to get us to try to understand and even feel a measure of sympathy for the creature. And it's a decently told story.
The biggest question here is: what ability did the creature actually have? The evidence onscreen doesn't suggest an actual shape-changing being because it's able to appear differently to different people at the same time. So it must be something hypnotic as well as the ability to create convincing illusion.
I also liked seeing the secondary characters getting something extra to do beyond their usual routines. I liked Uhura's somewhat flirtatious exchange with Spock. I liked seeing other little crew interactions besides those of the main crew. I liked seeing the life and movement of other people aboard. It was these little brief details, particularly early on, that allowed Star Trek to convey a convincing setting. We also saw Uhura at Navigation in the opening scene.
This isn't an awesome effort, but I think it's better than average.