The way Suzanne Collins apparently began writing 5 similar plots, was unable to choose one, and so stitched them all together to up the page count?
That Collins thinks Bad Things Happening to characters is equivalent to actual character development?
Katniss's PTSD overload?
Gale's creepy pick-up lines ("You only kiss me when I'm in paaaiiiin" oh cry me a river, Creepster Gale).
The fact that every character is cooler and more interesting than Katniss? Sorry, K-dog, but I'd much rather hear about Finnick and Annie and Johanna than about your closet naps.
Prep team torture storyline? Bizarre and extraneous and not followed through with? What is it with characters going through dramatic events and then dropping out of the story?
I know Collins was trying to work out a way for Katniss to plausibly kill Coin, but come on: President Snow lies to Katniss all the time. The whole "I thought we promised never to lie to each other" line is not the OH SHIT REVELATION moment readers are supposed to think it is.
Peeta would have been a nice Mockingjay. At the very least, he would have baked cakes for everyone instead of playing hooky in the supply closet.