The crucible of Jonathan Samuel Kent.
I can't speak for anyone else, but I felt like this issue played ZERO games and very rightly makes you uncomfortable and genuinely scared for Jon's situation on Earth-3. It's a legitimate trial by fire, and a test of a the sort of immutable will that would make Hal blush and Clark and Lois proud. It's mythic in its conception: trapped in a volcano prison while the mad god captor bares their soul at our young protagonist's feet. It's like something out of a Greek myth. Like waiting for a dragon to go to sleep before you escape its cave.
Also the imagery of Jon coming out from the volcano, ending up naked, and having to heal being symbolic of a rebirth/crossing of a threshold isn't lost on me.
Speaking more in terms of Superman: it's a warped and cracked look at our Clark. And I noticed that Ultraman's issues were basically those of our Clark deals with. This ties directly back to last issue where Jon was talking about the pressures that came with being Superman's son, and how he couldn't fully talk to Clark about it because he still saw him as infallible. Know it or not, Jon just learned how human his dad was in that via Ultraman of all people. It reminded me of how Waid recontexulized all of Superman's classic hand-ups in Irredeemable, and by proxy you "got" Clark more thanks to that book. What's kind of most messed up is that Ultraman seemed to care for Jon, and just wanted to talk to someone who could maybe understand him (somewhat similar to Jor-El).
I tend not to say "badass" often, but Jon getting out of the trap was freakin badass, and was a great set of durability, healing, and solar reserve feats to boot (if you're keeping track of that stuff). The kids ingenuity and overall smarts on full display here.
Geez my heart legitimately broke for Clark and Lois having to hear this. But the kid is something to be proud of, man. If he was ever gonna turn evil it would've been here. And to think, the little dude thought he couldn't live up to his genes.