I think the greatest trouble with Suzanne Collins' writing style is that she is PRETTY MUCH INCAPABLE OF SHOWING NOT TELLING.
She assumes her readers won't understand injustice and oppression and sacrifice and cruelty. So what does our friend do, seeing as those are the very themes she wishes to yeet at us in her books? Well. She literally spells out what the reader ought to see and think. She has Katniss explain how something is unjust, oppressive, sacrificial or cruel. It's almost painful to read.
That is like...that's one of the fundamental rules you never break when writing a dystopia. You're meant to portray Bad Things, but don't baby your readers, don't tell them WHY it is bad. Your readers are NOT BABIES! The only thing you'll achieve by taking this leaf from Collins' book (pun intended) is eliminate all subtlety from your writing, and seriously soften the punch that your story might otherwise have packed. That is the effect Collins has had on hER OWN STORY and it is SAD, guys. Look, I am going to give you an example of a dystopian story that played by the rules, withstood the test of time, and is still terrifying and sobering readers to this day.
1984 is so hard-hitting because the dystopian society in it is presented so...objectively, so impassively, all while STILL portraying the characters' weariness, their dreams of rebellion, their terror and their hatred. Orwell subtly raises questions through the events and memories and conversations he writes about, and neither he nor his characters answer them - like Katniss does in the Hunger Games). The world of 1984 is horribly vivid, everything feels real, and every stab at the reader's heart hits its mark.
As for the Hunger Games? Sure, it's scary and sad enough. I'd hardly be human if I wasn't at all affected by a 12-year-old being speared to death in a fight for her life. But the overall delivery is so...mediocre that the one time I actually felt horrified and moved to tears (so far in this series in which that is clearly the reaction I am meant to be having), was when reading about Darius' fate. Yeah, that random ginger Peacekeeper. Strange, isn't it, that the character who affected me most was a minor character? One with about four lines, no more? My best guess as to why that is, is that all the more important characters were ruined by the heavy-handed moralistic tone of Collins' writing. Darius was unimportant enough that Collins hadn't over-analyzed every aspect of his being in a way that effectively rendered him tediously redundant. His suffering felt real and crushing because it just /happened/ and he simply lived it as a real person would - no unjustified efforts to break it down and moralize it and explain it away.
I could go into greater detail about the way I dislike her writing style for its swift succession of monotonously similar sentences, the way it doesn't flow and instead feels jarringly rushed, leaving me wondering what the heck I just read. But I won't, because I think I've said what was most important. I hope you'll believe me, and be advised when reading this famous book. ...y'know what, actually, be advised when reading ANY famous book. Sheesh.