"Ultimatum" has a lot to live up to. For months, the build-up has promised big changes in the Ultimate universe, to re-invigorate it by "destroying" it. In this sense alone, the first issue does seem to be a success with several apparent and major deaths, conveying a definite sense of emergency.
For the most part, the plot hits the correct beats, throwing the characters into a difficult situation and allowing them to simply react as you would expect. It's reminiscent of Marvel's recent "quick start" approach to other event books, where everything is turned on its head in the first issue, leaving the "why" and "how" questions unanswered. In the sense that it leaves you wondering what happens next, the book is a success -- the problem, though, is that it doesn't feel like finding out is going to be a very good read.
Even before you've left the first page, the comic is full of strangely forced dialogue, with every panel taking pains to include the names of the characters depicted. It's obviously designed to give readers a quick "who's who", but in a medium where expository caption boxes and cast listings are possible, the artificiality of the dialogue seems both unnecessary and distracting.
And if the dialogue wasn't enough to give you pause, then the logical incongruities in the book are sure to -- at one point, some of the X-Men discuss which of them is the most "normal" looking, and somehow decide that it's Angel, because Dazzler's small number of piercings and tattoos make her less able to pass for human. It's a frankly baffling exchange, unsupported by art that makes only Nightcrawler look anything other than normal.
Art-wise, the book does offer some stunning pages, although as noted, the storytelling isn't always perfect. Finch manages to depict the sense of sheer scale of the disaster well, whether in sweeping urban vistas or the detailed depiction of smaller scenes, but an inability (or unwillingness) to draw characters without hyper-defined physiques negatively affects the appearance of the several teenage members of the cast. Elsewhere, further examples of incongruous art and script make the book an unsatisfying read, as characters frequently refer to a high number of dead civilians while readers see nothing to suggest it in the art.
While Loeb hasn't ironed out the flaws many found in his recent "Ultimates" run, there is at least a sense of moving in the right direction. Some weak characterization and dialogue notwithstanding, the issue has a comprehensible plot, and the events alone should be enough to make "Ultimate" fans stay interested.