The answer is to require a high percentage of test coverage. Then you skim through the code to get a general idea of what it does and how, then scrutinize the tests to verify they enforce that understanding.
This does three things. First, it prevents people from dropping big chunks of code and asking their reviewers to make it work (if coverage is too low, it doesn't work). Second, the tests spare you the cognitive work of verifying the code does it's supposed to--especially edge and failure cases. Third, this frees you up to think about the bigger picture. Is this the right way to do this, should we be doing it at all, does this conflict with something else in the works, etc
This does three things. First, it prevents people from dropping big chunks of code and asking their reviewers to make it work (if coverage is too low, it doesn't work). Second, the tests spare you the cognitive work of verifying the code does it's supposed to--especially edge and failure cases. Third, this frees you up to think about the bigger picture. Is this the right way to do this, should we be doing it at all, does this conflict with something else in the works, etc