Putting the human code review aside, one of the things I've been more impressed by during my time at Google has been the automated presubmits, generally the static analysis ones. I do a lot of Java, so Error Prone (https://errorprone.info/bugpatterns) has been a useful one (cf https://errorprone.info/bugpattern/FormatString); we have some others that Tricorder runs but I can't seem to find public references to.

One thing that's also an interesting challenge is the work it takes to make something a blocking presubmit: sometimes you don't get useful feedback from one, or maybe a test doesn't provide very good signal, and then people start force submitting to bypass the check because it's not providing utility, but in the process also skip other checks.