First issue we spend mostly in Limbo, and Magik gives us a tour of her backstory for those of you who had followed my colleague SpaceSquid's advice and stayed well away. Specifically: the bit about the dead X-Men littering Limbo (to your left is a bit of Nightcrawler's foot; on your right you can see Kitty Pryde's skull). I'll reply to some of SpaceSquid's points here (he hasn't done the thing for #4). So, SpaceSquid reads this as a morality play about ends vs. means, and he regards the idea (expressed by Storm and Magik) that using imperfect means - such as dark magic - to save - can possibly be described.
But it's not just a morality play. It's about actual demons and actual souls and actual dark magic. If you accept that logic of that using dark magic - even if for a beneficient end - can corrupt and deprave - then the rest follows. The soulsword is not a metaphor for the atomic bomb, and Magik is not President Truman. She is someone who is literally losing her humanity, her ability to empathise with others, and afraid to show herself to her friends, because of the acts of self-abuse she is committing. Whether or not it her actions are morally acceptable in their own right is besides the point. They come with a cost: can she live with it?
The answer here, of course, is no. She, the blonde girl imbued with magical powers and who has been fighting a very powerful figure who wishes to open a rift between dimensions so that demons might invade Earth, must commit one final action, of self-sacrifice, to close the portal, in the culmination of a long-running storyline. Her devoted sibling makes one last-ditch effort to talk her out of it, but fails. Oh, and the issue in question is called "The Gift". I've mentioned how Buffy-ish New Mutants is getting at this point, but this is uncanny.
Buffy died, but Illyana didn't take quite such an extreme measure. Instead, she survives, as if she'd never been to Limbo, had never spent those years there. ("The Gift" of the title, I think, rather than the Gift of death that the Buffy episode is referring to.) With that done, the portal closes and all is saved? But there's a back-up plan, shenanigans involving Baby X (Chris/Nathan/whatever) and Maddy Pryor.
Inferno the first proper complicated inter-title crossover that the X-franchise has really had: the massacre prelude was fairly minor; the Massacre didn't have any substantial shared scenes (you can't sensibly trace the comings and goings of the Marauders between series - I tried); and the Fall of the Mutants was just a parallel of unfortunate events (with oblig watching events elsewhere on telly). The meeting with their contemporaries from X-Factor plays out completely differently to the version in X-Terminators - and not just in the dialog and timing but different things happen. And this despite Louise Simonson writing both issues! I daresay this is due to the Marvel method: Blevins and Bogdanove must have gone different ways from Simonson's plot.
It would be an intersting exercise to steal panels from the four or five main titles here (changing dialogue where necessary) and see if you could put together a coherent Infero miniseries, to which the others are merely tie-ins. Artistically it would be an abomination, of course, but it'd have made my life easier, and that's really what counts, isn't it?