What do you know about tweetle beetles? Well ...Having used up the rest of The Hobbit in his previous movies, Peter Jackson had nothing left for this one except six chapters, some 50 pages, largely occupied by Smaug's attack on Laketown, the siege of Erebor, and the titular battle. We know how much he likes battles, so end to (nearly) end nonstop battle this movie is. So it's like tweetle beetles in that we don't see the characters do much of anything but battle and prepare for battle. There's also paddles and a puddle for good measure. It's also like the tweetle beetle battle in being a giant muddle.
When tweetle beetles fight, it's called a tweetle beetle battle.
And when they battle in a puddle, it's a tweetle beetle puddle battle.
AND when tweetle beetles battle with paddles in a puddle, they call it a tweetle beetle puddle paddle battle.
These six chapters of the book include four songs. There are no songs in this movie. There is no consideration of audience knowledge, either. Viewers who aren't familiar with the book had better remember the earlier movies pretty well if they hope to make any sense at all of most of this. Nor is the title ever explained. In the book the five armies include the Wolves. There are no wolves here, so the uninformed viewer may be baffled about the number. The orcs have two separate armies; does that count? Is Thorin's band a separate army? How about the Eagles? So it could be any number from four to seven.
In the previous movie, Jackson threw the entire relevant chapters of the book away, leaving only the character names and a paragraph's worth of plot structure. He's nowhere near so cavalier in this one, so the changes clang more. I started out by noting that the people of Laketown evidently believe they're located on the River Anduin, which is actually on the other side of Mirkwood; that the arguments in the conflict over who gets the treasure are sufficiently tweaked that I predict it will confuse future students of the book in the way Jackson has confused them over Aragorn's attitude towards the kingship; and that, when Galadriel rescues Gandalf and Radagast from Dol Guldur - OK, that's another change - she vamps out, the way she did in Jackson's Fellowship, and, if I'm reading the imagery accurately, disembodies the Necromancer, leaving only the vaginal slit famous from the LotR movies. I'd guess that somebody told Jackson he had been in error in depicting Sauron as a helpless disembodied eyeball, so he has concocted this explanation as to how Sauron got that way.
After that I stopped keeping track, though it was hard to miss the Elven-king's parting advice to Legolas to seek out a Ranger called Strider, although at this point in Tolkien's history he was still a ten-year-old boy in Rivendell called Estel. Bilbo, very much a supporting character in this story - what a waste of Martin Freeman's considerable talents - gets to say "The Eagles are coming," although not until long after they'd dramatically arrived, and he mutters it without anybody within earshot, so as a dramatization of one of the great "book moments" it lacks effectiveness.
Basically, book fans trying to find moments to squee in delight at will feel like they're trying to suck through a straw at an emptied glass. Bard doesn't apostrophize his black arrow. The language of the negotiations at the Gate is softened into pudding. Bilbo's farewell to Thorin has most of the words, plus some unnecessary ones, but the context of the scene is entirely different, so that didn't work as a "book moment" either.
As a wall-to-wall battle movie, I found it tiresome. All the armies move in mechanized lockstep unison, even the Elves putting their arrows away or the Dwarves hastily erecting a wall of shields. Scenes like this dwell in the Uncanny Valley. The Orcs outweigh the good guys so massively that in order to keep some kind of equilibrium, they have to be ridiculously easy to kill. The Elven-king swipes the heads off a whole line of them with one stroke while they're clinging to the antlers of his moose (heroes riding ridiculous choices of animals is another continuing theme in this movie), without even damaging the antlers. This applies until the painfully prolonged Single Combat Warrior battles against the monster commanders Azog and Bolg (Azog and Bolg, eh? Book fans, shake your heads again), who are, by contrast, ridiculously difficult to kill, so it goes on and on. Legolas climbs up rocks falling through the air. "Oh, come on," in the words of Dain finding that the first orc army has entered the battlefield by tunneling through the mountains with the help of giant Were-worms, the ones mentioned by Bilbo back in chapter one. As Jonathan Fischer points out, Dain says this so that you don't have to.