Some say code reviews prevent bugs. They are wrong. Testing code and static analysis prevent bugs. Require all code to have unit tests and run them automatically. Run static analysis automatically. If you have developers who don't write tests, fire them. Code reviews only give you a false sense of security. You figure: since two people looked at it, it therefore must be good; forgetting that the reviewer just skimmed it over to get it out of their queue.
Some say code reviews enforce style. Assuming you care about style: why not just have your IDE or static analysis tool enforce it for you?
Some say code reviews help share knowledge. That may be true, but it should be unnecessary. Standups share knowledge. Wikis share knowledge. Comments share knowledge. Code should share knowledge. If you have code hitting trunk that every developer on your team can't understand easily and quickly, then you need to start finding new developers.