This is how we do it (using Stash). Most reviewers are across the code base and so essentially rubber-stamp approve. External stakeholders (mostly operations) go over the code with more rigor since this is their one shot at getting errors corrected. "NBC" (non blocking comment) is used to describe a nit-pick (formatting, suboptimal but not awful variable names) that isn't amenable to automatic linting. Additional review comments are assumed to be blocking and require at least an acknowledgement. Big changes are usually acknowledged with a "my sprint is in danger" and put into the backlog.

I've mentioned it in previous threads, but we try to prevent hostile reviews by separating the code from the coder. Comments should not reference the author, only the code.