I know the aggravation of getting a hairball of code to review, but I often hold my nose. At least find a better reason to send it back, like a specific bug.

If you're sure cyclomatic complexity should be minimized, I think you should put such rules in a pre-commit hook or something that runs before a reviewer ever sees the code. You should only have to help with that if someone can't figure out how to make it pass.

If you're not willing or politically able to implement that, you might be wasting time on your personal taste that the team doesn't agree with. Personally I'm pretty skeptical of cyclomatic complexity's usefulness as a metric.