The acting is fine. The rest is pretty bad.

Rating: 4/10 (28 August 2017)

I never write reviews, but this movie prompted me to.
There is some pretty bad writing in The Number 23:
Carrey, Narrator: "Time is just...numbers with a meaning attached to them."
Carrey, Narrator: "She said she was a good person once. But now?" Suicide Blonde: "I'm a bad person." -- I laughed here.
Carrey, Narrator: "I was right. She was in danger. I just didn't realize the danger was me."
Later, Carrey tranquilizes a dog in a cemetery. A priest and a groundskeeper (the dog's owner) come out of nowhere, and Carrey asks the groundskeeper why he named the dog Ned. At no point does anyone ask why this man is shooting dogs with tranquilizers (he doesn't identify himself as animal control). Instead, they answer Carrey's questions and chat with him like a casual acquaintance.
Anyway, I have to mention the pacing of this movie: It's probably one of its biggest flaws. Like 25 (23??) minutes in, Carrey's character is essentially a firm believer in the whole conspiracy. That. is. WAY. too. fast. The movie doesn't try at all to get you in the main character's head-space. So at 37 minutes, when Carrey asks his friend, of the number 23, "is it God?" I couldn't help but roll my eyes.
It's not only how fast Carrey "believes," it's how little it takes for him to be pushed off the deep end. Carrey's two characters are drowning in a bunch of confirmation bias, which comes across more as ridiculous than spooky or suspenseful. The Hiroshima bomb was dropped at so- and-so time, which adds up to 23. Okay? What time was the Nagasaki bomb dropped?
On the topic of the plot: It's much too easy to foresee the twist ending just shy of the hour mark. In the movie's book, the murderer (Carrey) gets away because the lover senselessly picks up the knife and gets his finger prints on it. At 55 minutes, Carrey says that the killer in real life from 15 years ago was discovered because his finger prints were all over the knife, HEAVILY implying that the convict, like the character in the book, was framed.
There's also a major plot hole at the end of the movie. The hospital that Carrey is committed to runs through his family history, finding out that his father committed suicide. They don't, however, find that his longtime girlfriend was recently murdered by stabbing? A nearly identical case to the one in his book?
Also a bus almost runs Carrey over at the end because it never slows down, despite seeing Carrey in the street from at least half a block away. Then it speeds on by when he steps out of the way, like a train would.