There was an excellent article on this by a formal Interactive Fiction reviewer who reviewed Spring Thing, but unfortunately I can't seem to find it right now. He basically said that on a scale of 1-10, he rated things as follows
0-4: Game that is a pain to experience, which intentionally or unintentionally makes you resent the time you spent on it
5-6: Game that checks the boxes of basic plot, basic characters, maybe a few common tropes, and ends, however unsatisfactory the experience. A limited number of people will enjoy this, it's usually something you'll play if you have absolutely nothing better to do. This is an easy score to obtain, assuming you aren't an idiot.
7-8: A game that has a solid foundation, an innovative idea or two, but does not stand out on its merits. Often these games are follow ups of successful ideas that do not however become strong enough to outstep the shadows of their predecessors (for which reason a person who hasn't played its predecessor may enjoy this game a lot more than a person that has)
9: A game that has innovative content, a strong narrative, and multiple occasions which delight the player. This type of a game usually takes years to make, and has been through hundreds of iterations, and is polished through the grind. These are the types of games you'll refer to while thinking of lesser games. However, at this point and beyond, games pretty much have all the boxes ticked for competence of story, and it's now themes and personal opinions which affect the score. The importance of the game resounding with a person's own views is why Gamespot rated GTA V an 8/10, while others were screaming at it being a 10/10 (Personally I agree with the 8/10 assessment from a story perspective, the scripted part of the game really was a pain to play)
10: A unicorn. A once in a decade experience, in most cases. A game that redefines what you can expect from the medium, that inherently reinvents a concept. It has more quality and depth in one of its parts, than many full made games could dream of. It also tends to be an easy recommendation to nearly anyone you can scream out. Depth of experience is usually required for this, so The Witcher 3 gets this rating near flawlessly, while something like Rocket League (Innovative yet limited) will be penalized for its limited scope.
In CYS terms, I understand 1/8 means the game is broken to the point that there are no links, or something equally terrible/pathetic. 2/8 > Extremely short and generic, 3/8 > Has a story marred by various problems, or is often so short the game leaves no lasting impression on the reader, 4/8 > Game had a few interesting moments and was mostly grammatically correct, 5/8 > Game had a fair length or breadth of experience, and you will most likely remember playing this game, 6/8 Game with expansive scope and great depth of experience, written by a skilled mind, you'll recommend this to friends, 7/8 > Exceptional writing and depth of experience, the author has thought of and planned events you may never have come across on your own, and at each turn there's something interesting, you'll be recommending this to strangers willingly. 8/8 is a unicorn that cannot exist, due to the way rating works (someone somewhere is going to give you a less than 8 score), it would probably something written after years of effort and be archived for posterity.
In case you're looking for resources on how to make a storygame, I recommend this thread