Bad acting. But it could be because of the actors having to interact with nothing/cgi. But even then the acting human to human is pretty bad. The pokemon world doesnt feel authentic. At one point detective pikachu called a group of Aipom monkeys. If this world is full of pokemon only then how do they know about monkeys? Monkeys are a real life animal. Calling aipom monkey kind of breaks the immersion. Ryan Reynold really carried the movie but I hated almost everything about it. Oh and also the movie is rated PG but they have references to pouring gasoline on pokemon and lighting it on fire. Also they loosely reference cocaine..so yeah.. I would give it a one star but Ryan reynold really carried the movie and sometimes I laughed at pokemon activities like lickitung licking people's face. Other than that you could forget about this movie. "Forgettable " is the perfect word to describe this movie. Too many exposition and Forgettable characters. Character development is pretty bad too.
Edit: I just finished the movie and I got to say the ending kind of made up for it. But I wish the entire movie could have had more of that ending energy. Feels like that last part was, again, fully carried by Ryan Reynold. Felt like the entire movie except the ending was written poorly and Ryan just fixed it at the last second. I don't think anybody else could have pulled off his role. It really wasn't fair to the other actors and actresses in sorry. Ryan is a really good actor with tons of experience