Ok, I had multiple thoughts while watching it and after watching it. Here they are. Spoilers: They aren't particularly good.
Let's start with the good things: I mean, the first scene in the office is ok, from the 2nd book. But... That's about it tbh. Can you think of any other good moments from the film or good aspects, because if so I'd be interested to hear them.
Now the bad things... Let's start with the storyline and plot. This infuriates me so much because it's so completely different. They took away the mystery of Artemis's father, choosing to make him likeable or, relatable, but Artemis isn't meant to be like that. He's treated far too much like he's nicer, and he's not in the first book. Nor is his father in it, but I'll get to that in a minute.
He's meant to be a genius mastermind, but I get little evidence of that from the film, and I don't get that feel from the actor. Whether that's a fault of the writer or the actor, I can't say. He's meant to be intimidating, which he's not. His relationship with his father is completely screwed up, having less of a businessman feel and a closer relationship. He's meant to have gone missing years earlier, and is motivation in the first book, not a character.
On the topic of his father, why does he know about the fairies?!?! Oh, and he worked with Holly's father, again, I'll come back to that. He shouldn't know and should be absolutely clueless. He was taken by the Russian Mafia (Correct me if I'm wrong bc I'm not 100% sure about that) - not Opal Koboi (Come back to that) which is the entire plot of the second book. What ya gonna do then Disney, keep on making it up as ya go along?!
Holly's father died when she was young, he wasn't special, and he didn't work with Artemis's father. He wasn't supposedly guilty of anything. That presumably happened because Holly needed motivation, but she already had that in the books being the only female LEP operative.
Opal Koboi is far too vain to wear a mask or use a voice-changer. And she doesn't appear in the first book. End. Of. Story.
Now lets address the biggest issue: THE MAGICAL ACORN. Seriously Disney, what were you trying to do here? Just what? It seems too fairytale for the generally older audience of the Artemis Fowl books.
To sum up, it completely separated from the books. What's most infuriating is people who haven't read the books think it's great, but they don't have the full context. Please let me know your opinions, it'll be interesting to hear if you disagree with me and get another perspective.