As someone who loves the film:
(1) Inconsistent acting, the teenage Arthur who practiced on the beach was a terrible actor.
(2) Some of the dialogue lines are cheesy and over-the-top (for example the conversation about tears). Some of the lines are on-the-nose, delivering exposition in too blunt of a manner (which may explain #1 partly).
So the film wasn’t perfect and it has hiccups (this is coming from someone who’s probably seen 80+ films in theaters in 2018 and consider it to be #10 in my top 10 in with mostly indie films just because it’s a fun, wild ride that one can watch on repeat). But with that said, while in scholarly film terms it needs work - on a fun scale it soars.
Critics are coming at it from the scholarly approach since they’re expected to, but even many of the harsher ones said they had fun. It’s a classic popcorn film in the greatest way possible.