... doesn't seem very climactic to me. If they follow the book, all is quiet until Bilbo convinces the dwarves to shut the door. Then Smaug comes along and smashes rocks.

I could see it going either way, but I would like Smaug's death to be the climactic scene of DOS. I would reverse the orders of chapters 12 and 13 to put the exploration of the treasure in TABA and the death of Smaug in DOS.

I would also like to see the battle with the necromancer play out in TABA. I think the defeat of Smaug is interesting because it is done by humans (Bard) as opposed to the greater powers of ME (Gandalf). If the Bo5A is part of a greater plot, it climaxes for both the lesser (Hobbit/Dwarf) and greater (White Council) arcs. If the white council "wins" in DOS, I feel like the significance of the Bo5A is diminished. It makes the land more peaceful after the defeat of a great host of goblins, but the big picture is the necro AND the goblins (plus, to a lesser extent, Smaug). I don't want to resolve the big picture before the little one, especially not in two sequential films.