No Mutants Allowed

At the climax of the movie L just chases Light around with a gun (while running hilariously) you know, L's classic Deduction revolver he always carries with himself.

Wow.... that bad, eh?

It's a movie written by the kind of people who think "Deduction" is just making blind guesses that are right by coincidence and that being smart is just being omniscient.

... Oh no. What is white washing?

Well, aside from making most of the cast white (which is shitty but the least of the movie's problems) they also wattered down the themes of the series and characterzation so they can fit a more generic Action movie mold. Kira has been sanitized beyond belief and isn't even smart. And Ryuk, because of his status as a "Death God" was made more akin to a devil, more antagonistic and EEEEEBOLLL.

They also think adding "Fuck" to every other sentence makes the dialogue "Mature". Not to mention they turned Light's manipulation of Misa into a straight up teen romance subplot that is as cringe inducing as the worst of them.

The filmmakers probably never actually bothered to research on the original works. Even the live-action versions from Japan at least show some understanding of the work (though the 2015 TV series is probably what inspired the further dumbing down of Light & added antagonism of Ryuk). That said, the 2015 version still sounds far better (plus that series better depicts Light's fall into madness and megalomania).

L chasing Light with a pistol to bust a cap on his ass. That says enough.

The portrayal of the powers of the Death Note is also very inconsistent. First time it just looks like it controls probability to create Final Destination style deaths (which I have no idea how Light even manages to take credit for seeing how they are all accidents instead of systematic heart attacks)