I really enjoy code reviewing, and maybe I'm weird but I especially enjoy CR'ing huge PR's. It's like a puzzle to figure out what's going on and write advice in a way that is clear, constructive, helpful, and appreciated. And when it's a really good PR it's even more fun, seeing people make great progress and do great work is truly enjoyable.
It can also be challenging though, especially preventing it turning negative if there is need for big changes. Also making judgement calls of what matters and what is nitpicking. Imo it's essential to stay on the conservative side as nitpicking is a giant waste of time and incredibly demotivating.
You mention reining in, which doesn't sound fun. What you might try is to find ways to not say "no" but actually demonstrate or teach why you might or might not want to do something, or just focus on the alternative. Basically challenge yourself to find ways you can give people the opportunity to learn the lesson themselves in an engaging motivating way, instead of having to hold them back. Also maybe let some things go, not everything will cause disasters.
Few more things I find work well;
- Outside of normal work learning activities; workshops, presentations etc. (let them present as well)
- Solicit feedback yourself; Create an environment where it's normal and appreciated.
- Give "optional" advice, give them the choice to follow it or not.
To come back to your question; I find it really challenging at times, but definitely not boring. I think seeing it as a challenge might generally help to find the joy in it.