"Earth X" was the story of an alternative Earth in which creators Alex Ross (story, character designs, epilogue and covers) and Jim Krueger (story and scripts) came up with interesting twists on the Marvel universe. There is a sense in which "Earth X" was a flip to DC's "Crisis on Infinite Earths," where the goal was to reign in the expanding universe of comic book characters and worlds into something more manageable after decades of stories. In contrast, the whole idea of "Earth X" was to damn the torpedoes and make everything fit (e.g., the gods of Asgard). I would hate to pick up "Universe X, Volume 1" without having read "Earth X," because a lot of what is happening here (e.g., who is dead and kicking) will make no sense to you, so you have to read the first part. On the other hand, I can see why some fans will be disappointed when they get to this middle part of the trilogy, which takes a much more episodic approach, with most issues focusing on a particular superhero. You get an idea of this when you see that Volume 1 collects the first half of the "Universe X" story, with "Universe X #0-7 with new Appendices, "Universe X: 4," "Universe X" Spidey," and "Universe X: Cap."
To make the long story of "Earth X" short, Terrigen Mists had turned pretty much everybody on the planet into super beings. The Celestials come to destroy the Earth by releasing a Celestial embryo but the planet is saved by the new Galactus (nee Franklin Richards), who consumes the egg. Reed Richards, who has been pretending to be Doctor Doom, creates a vibranium network of "Human Torches" to burn off the Terrigen Mists and thereby restore Earth's human population. Whether this would be a good thing or a bad thing remains to be seen, and as the "Universe X" part of the trilogy begins Earth is on the brink of a civil war. Losing the Celestial embryo has reduced the planet's mass, causing shifts in orbit and polarity that have resulted in climatic changes more akin to "The Day After Tomorrow" than "An Inconvenient Truth." Not surprisingly, the mass of humanity does not want to give up its powers and those Marvel superheroes left alive and now fighting those they once protected.
The main narrative thread throughout these stories are Captain America and the reborn Mar-Vell are on a scavenger hunt to collect the greatest sources of power in the world (e.g., the Books of the Darkhold and Vishanti, the Mandarin's rings of power). But there are separate issues dealing with Reed trying to bring Sue back from the storm, Spider-man and Spidersman, and what I would call the final fate of Captain America except for the fact that in this storyline the dead live on and fight on in the land of the dead where they all think they are alive. I am not sure if this view of the realm of the dead is a telling allegory (comic book superheroes never really die), or whether this variation of Valhalla is just a major flaw in the story. There may be relatively few deaths in the world of comic books, but those deaths usually matter, and this idea undoes that. There are deaths in these stories, but we are talking about deaths in an alternate Marvel universe so it is not real (in addition to being not "real").
John Paul Leon has been replaced as the penciler, so "Universe X" has a different look. Doug Braithwaite and Thomas Yeats and the main pencilers this time around, with Jackson Guice doing the layouts on "Spidey" and Brent Anderson doing some pages as well. Bill Reinhold is inking again, but Al Williamson gets equal billing in this trade paperback and there are a whole bunch of other inkers credited, including John Romita Sr. who does the "flashback" pages of the "Spidey" story. The plethora of artists only reinforces the idea that this is not as coherent a story as the first part of the trilogy. I do not think the results are great or particularly memorable (although certainly some alternative reality comic book stories can be) and I become less and less interested in the appendixes to each chapter as we go merrily along, but there are some interesting elements to be plucked from the complex narrative, such as the idea that the biggest bad guy of them all would end up being Crusher Creel. I already have "Universe X Volume 2 TPB" and have pre-ordered both "Paradise X Volume 1" and "Paradise X Volume 2," so I am going to see this trilogy through to the end.