I'm an SRE, which means most of the code I write isn't directly user-facing, and thus isn't normally subject to hard external launch deadlines. That means I'm rarely rushing to push my changes through on a tight schedule. If there's a production emergency and I need to make an urgent change to avoid or mitigate an outage, there are escape hatches at our disposal to temporarily circumvent the code review system when no one is immediately available to do a review, but the need for that is pretty infrequent.

I rarely find it frustrating. On the contrary, I really appreciate Google's emphasis on code quality, even though it does come at the cost of some agility. I used to work at a company where the implementation of code reviews was generally resisted, and though we did get new code out the door faster, we ended up with some real maintenance nightmares as a result.