Broken Base: Whether or not the film is a good adaption, if even a good movie on it's own.
Genius Bonus: Digger, who speaks with an Australian accent like most of the band, becomes accepted as a guardian and therefore a soldier with the rest of the band at the end of the film. So in Aussie slang that would make him a Digger Digger. Who digs.
Kludd moonblinks his baby sister, which is essentially zombifying her. Seriously, dude, NOT Ka HOOLE!
Nyra crosses it we she manipulates the above owl into her own Tykebomb.
As for Metalbeak, trying to kill Ezylryb in front of Soren.
Nightmare Fuel: The movie is chock full of it, including: Allomere getting dragged off by vampire bats, the bats themselves, the Battle of the Ice Claws (Deleted Scene), Kludd falling into a raging fire while screaming in terror, the moonblinked owlets, etc. Really, it's surprising that the movie doesn't have a HONF page yet.
So Okay, It's Average: Despite the drop-dead gorgeous animation of the film, it suffers from the narrative trying to tell an epic story akin to The Lord of the Rings in the span of roughly 90 minutes, which ultimately just falls flat and leaves it as more of a Cliché Storm instead, which is probably why it's not remembered much.
Tastes Like Diabetes: The ending borders on this as it really goes its lengths to describe how perfect everything is, and how Soren and his friends were crowned Guardians over night even though it was earlier narrated how such a position took years to strive for.
They Changed It, Now It Sucks: The film was not well received by fans of the book for its multitude of changes, like Kludd and Metalbeak being split into 2 characters, Nyra showing up despite only appearing in book 4 onwards (due to the film taking the plot of the first 3 books), turning Digger and Twilight into comic relief, several characters from the books missing, or having their species changed, missing key locations from the books, and certain characters being saved/killed off when they weren't in the books. Duckyworth would become one of the most prominent (and vicious) critics towards the film. (Heavy spoiler warning for the first 3 books and the film in the outgoing link.)