As I've probably mentioned a few times here, I don't really think of myself as a reader DC comics; I think of myself more as a reader of Batman comics. Plus, I only really started consistently reading Batman four years or so ago. As such, I'm really not familiar with all the various "crises" that DC has used from time to time to clean up its multiverse.
The good news, though, is that Johns is familiar with these crises, and he does an excellent job of using this issue to introduce them to us. He uses Metron (the DC equivalent of a Watcher, as I understand it) to review their history and let us know that the repeated collapses and births of reality that they've caused threaten existence itself. We learn that, in the past, he's been willing to break his non-interference vow to save reality. For example, he engineered a pact between Darkseid and the Highfather to end war between them, since it threatened reality at that time. (Actually, I wasn't 100 percent clear on this part. I think that he's saying that a war between Apokolips and New Genesis would've destroyed reality, but it's also possible that it could've just somehow interfered with his ability to perform his duties. I may need to do some Wikipedia research on this front.)
Now, Metron wants to engineer another pact to save reality. He worries that the Anti-Monitor (apparently the cause of the original crisis) is once again going to try to destroy the Justice League's universe, as he did the Crime Syndicate's Earth. (I'm not entirely clear on why he hasn't destroyed the Crime Syndicate's universe as well as its planet. Also, we learn that his destruction of their Earth apparently opened the hole in the multiverse that Brainiac is exploiting in "Convergence," but Johns doesn't explain exactly how that happened.)
Surprisingly, we learn that Anti-Monitor was Metron's predecessor, but, somehow, became a destroyer as opposed to an observer. Metron makes his offer to the Anti-Monitor: he'll put aside observing to find a cure for the Anti-Monitor (so that he's no longer a destroyer) if he agrees not to destroy the Justice League's universe. He tells the Anti-Monitor that he has foreseen that his path will bring him in conflict with Darkseid. However, the Anti-Monitor has a surprise up his sleeve: Darkseid's daughter (whoever she is) blasts Metron from his chair, and the Anti-Monitor reveals that he actually wants a war with Darkseid, implying that it'll save him.
For long-time readers of DC, this issue was probably super dull, but I have to admit that it really helped me. I understand the basics of the crises better than I did, and I'm really ready to fully engage with the upcoming "Darkseid War." I haven't been this excited about "Justice League" in a long time.
**** (four of five stars)