Finished the book. Pretty easily the best since the first. As with the others, a thrilling read, the story moves, chapters end on fun cliff-hangers, and the characters and locations are well-drawn.
Minor spoilers but mostly nothing that won't be revealed in the inevitable movie trailer:
It covers yet another Hunger Games, but this one feels much different -- if the others we've read about were Super Bowls, this is an NFL Championship Game with leather helmets. The differences made it feel fresh. There's some new world-building, too, but not so much that it overwhelms the story.
The author learned from Mockinjay -- it's obvious this is meant to be split into two movies, each with its own story arc. That said, the first movie is the better one. Investment in the characters carried me thru the final third of the book, but the screenwriter and director are going to have their work cut out for them padding that story to 2 hours without it feeling like obvious padding.
And, in an abundance of caution, potentially more potent spoilers about the book as a whole, but none of the surprise plot twists, nothing that will really impact your enjoyment reading it:
This isn't Wicked/Mysts of Avalon/Maleficent. Snow isn't a misunderstood hero, he's sympathetic at times but clearly a bad guy from the start, and this is his journey toward super-villain status. But because the story is from his POV, he doesn't see himself that way -- we see his (twisted) motivation and self-justification. He's so well-written you go along with it, even root for him at times, but he's never not the total bastard we see in the original trilogy.