There are certain phrases people use when describing fiction that sound clever without saying much. "Social commentary," "world building," and "flat characters" all give an impression of refinement, but they're rarely if ever delved into. Usually it's better to avoid these phrases and say what you mean in more detail. Using the phrase doesn't make the review sound any savvier to me.

It's a bit like the word "utilize." You didn't notice all you said was "use"? "Utilize" is "use" + "I'm feeling self-important." These other phrases also risk betraying self-importance rather than meaning.

Instead of referencing "great world building," why not say what's great about it? Instead of "there's so much social commentary," why not paraphrase what the commentary is saying here and there? You didn't like the characters much? "Flat characters" sounds as if you know what you're talking about, but it's rarely justified. More often than not, it's a fancy way of saying "I didn't like the characters."