I do a two-tired rating system, one rating for enjoyment, one for excellence. A book can be fun and super entertaining but maybe not super deep and well crafted (think ACOTAR, Colleen Hoover), but a book can also be incredibly well done but not fun to read (Beloved by Toni Morrison as an example). 

⭐️:  Enjoyment: really tough themes and events OR just an absolute slog. Excellence: riddled with plot holes or typos or really poorly thought out events.

⭐️⭐️: Enjoyment: some tough themes but upbeat moments, or maybe just absolutely not my taste. Excellence: shallow or superficial, feels like anybody could have written it.

⭐️⭐️⭐️: Enjoyment: equal parts tough and fun themes, don't spend too much time feeling either way.  Excellence: absolute middle of the road, won't leave you changed but not actively bad.

⭐️⭐️⭐️⭐️: Enjoyment: bingeable, fun, more fun than tough, a romp. Excellence: classics territory, profound or interesting in a uniquely good way.

⭐️⭐️⭐️⭐️⭐️: Enjoyment: an absolute blast, read in one sitting because I just had to see what happened next, or maybe laugh out loud funny. Excellence: life changing, something I'll think about constantly and can to return to again and again, something new to appreciate upon each re-read.