Just like the last 2 films and all 3 books...
The books are both social satire and dystopian sci-fi action works. All three follow a similar model and there is a symmetry there. Most of the stories are spent on the world-building, the characters, establishing the stakes and political workings, steadily cranking up the tension...and then the end of each book has the action climax that provides the visceral catharsis for the build-up in each book.
There is a progression there, too, in the climaxes, with the first Hunger Games getting its script flipped and rules deconstructed by the Quarter Quell in Catching Fire and then that taken to a whole other level by the action climax in Mockingjay, which isn't a game at all...or is it? This progression directly connects the sci-fi action arena element to the social satire, or I should say broadens it into that realm, and suddenly you realize that you're watching films about all our wars and about what happens when systems of control create counter-systems and the collateral damage involved, not to mention the question of whether we're ever really free of that control.
Splitting Mockingjay into two movies doesn't necessarily undo that progression, but it does undermine the structural elegance with which that progression is conveyed in the book trilogy. It also creates two separate chapters of the third part of the triptych, each lacking necessary elements to their arcs and stories. Part I has all the building without the pay-off. Part 2 will be the pay-off without the building. Both the first movie and Catching Fire contained both of these elements and so they felt like whole documents despite only giving us one panel apiece of the triptych. the Mockingjay is a document divided, even moreso than the final Harry Potter or Hobbit movies as those flicks contain multiple thematic and dramatic arcs and many action beats. the arc in Hunger Games is more singular and the great majority of the action all comes at the end.
i do look forward to seeing Part 1, i just don't know if i can justify the movie ticket expense. catch it on video, watch Part 2 in the theater, that's my plan like many others here. i really loved what Lawrence & Lawrence did with Catching Fire, so i'm sure whenever i do see Part 1 i will find it a very well done movie. i'll even probably consider it a good film. just one that's fundamentally incomplete and unsatisfying from a storytelling perspective, and lacking the action from a narrative construct where the action element is absolutely crucial.