The characters are not simply 'types' or 'archetypes' which we may subliminally take note of (i.e. innocent daughter, villainous official, fugitive) as we engage with the plot, slotting this story into expectations formed from earlier, similar films.
Nor is the story itself a re-setting of a prior, famous tale, 'updating' or 'refreshing' deep themes (i.e. King Lear re-done as Kurosawa's Ran).
IB isn't a simple story of revenge based on cruel treatment -- that would require a realism not attempted or claimed. We don't have characters real enough to feel human toward. The audience response is expected somehow else, commonly-stocked and easily-bought.
The movie is meant to be comically violent. This is burlesque -- vulgarizing for laughs (or 'laffs') something otherwise possibly having worthy edges. This handling lowers values, bringing the significant -- including monstrous enemies -- down to a low level.
Yes, there is satisfaction to be gotten out of watching Hitler's face machine-gunned into a goo-that-was. We still reverberate from the 20th Century, continue to ask for psychological remedy. But this is lowest-common-denominator yuks. Sardonic: as bestial or more than the beast being overcome.
Perhaps I do a disservice to 12-year-old boys, but the film aims at an audience level of their (quarter-)sophistication.
Nota bene: This is not to validate self-righteous snobbery. We all have 'guilty pleasures', and someone liking IB might do so simply for the presence of Brad Pitt, or for the fact that the scenes are called 'chapters', or for the reason that one saw it the night of getting a better job.
But that's not aesthetic judgment, whether an effort makes or fails its artistic attempt, and has attempted enough.
Artistry is more than conforming to professional production standards, and has no direct relation to profit.
And artists, however self-expressive, have a responsibility -- to themselves, at least -- beyond just spewing-up their stomach and liking what they heave because it smells like them.
Art's an activity worthy of being done, serious even in its play. If the motivation lies elsewhere, if it's held up short of that, stop. Don't go further.