Of all the different kinds of games I've reviewed, the genre I most dread assigning a star rating to is interactive fiction (gamebooks and the like). I'm speaking now as someone who teaches graduate-level creative writing classes as part of their day job.
I evaluate whether a story is free of grammatical errors, I can consider the specifics of an author's style and how it relates to the genre they're writing in, I can analyze the structure of the story and the development of it's characters, I can point out cliches, genre conventions, inaccuracies, oversights, and potentially-offensive bits. If you're a student of mine working on an assignment with specific expectations, I can assign you a grade.
But reviewing? I can describe who I think will or won't want to play a given gamebook (trying to figure out who a game is and isn't for is one of my favorite parts of reviewing), and I can discuss game mechanics (which are a little closer to objective than story), but if it's a well-told story lacking in technical and grammatical flaws, you're still talking anywhere from 3-5 stars depending on how well someone likes the story being told.
I usually consider a one-star difference in rating to be the reasonable differential between reviewers operating on the same general principles. With games that rest almost entirely on story, you have to double that.
For comparison, movies (where there are a lot of semi-obejctive elements, like costuming, makeup and actors' performances) and restaurants (where there is always a genre of food to compare a given meal to) get reviewed on a star system, but journalistic book reviews come with a recommendation (or the opposite), but almost never with a star rating.