In a nutshell, the story is about a millennia-old psychic vampire called Selene raising an army of superpowered dead to bring abouther ascension to godhood. It's another one in a line of threats that faced mutantkind in Marvel Comics' X-Men/mutant line of books. The mutants are but a couple hundred now and nearly all are gathered on artificial island Utopia, off the coast of San Francisco, where it's convenient for editorial to have threat after threat pile up, I suppose.
Contrary to most crossovers, though, this is neither a line of issues from different series which directly follow into each other (horrible if you'd usually read or collect only one of the books), nor an event based on a main series with spin-off one shots and miniseries (generating a plethora of bad, useless books). There's an opening one-shot setting up the main story, which is carried out in X-Force, of which you have a coimplete 5-issues arc. Short stories from that opening specials set up the arcs from New Mutants and X-Men Legacy that follow, completing the crossover by telling all facets of the big plot as at least partially seen in the main issues. It's perfect for readers of the individual series, who might have picked up only their usual book and still have gotten a nice completed story, and for trade-buyers, who get the complete package at once, in easy to read chunks.
The DVD-like extras include two relevant back issues and short stories introducing the cadre of villains helping Selene in her quest, mostly X-Men drop-offs/ex-villains with a grudge and an instinct for killing that makes them perfects to execute Selene's plan.
It's a nice story, with X-Force delivering especially good art and New Mutants delivering deep, solid writing, but everything is above average and there are very nice artistic surprises in the short stories as well.
Story-wise, the extras aren't that relevant, but I don't think the colleciton would have costed less without and some of the back story there is still quite useful.
As a reader who'd wish mainstream comics were more accessible to any audience (comics fans or not), this looks to me like a great example of how to do these large stories right, and also how to collect them in an intelligent, reader-friendly (price- and story-wise) way.
A question still lingering in the air would be: would you continue buying the individual series, or pick up back issues/collections? Here are my 2 cents: Definitely for X-Force, I like the characters, the stakes in the book are high enough for me to care and the art is gorgeous; possibly for the New Mutants, if they keep writer Zeb Wells on hand, since he's the true hidden gem of the collection, a good and underrated writer. X-Men Legacy, though, fails once again: The sotry is told well enough, but I don't believe writer Mike Carey has any good handle on superhero comics. He tries to push his ideas, does the usual awkward bit in a crossover in which some writer shoves "character moments" into these dynamic stories, where they end up looking stunningly put of place, making characters look stupid or crazy, pulling you out of it and not adding anything of true relevance. Carey has a way of trying to push his sensibilities in chracaters he doesn't really understand and, since he's no good at superhero "logic" or science fiction, the most used phrase in his X-men scripts seems to be "some sort of".
However, he manages to tell a decent story with classic X-villain Proteus and the artwork saves him in most places. These mere 3 issues do not detract from the overall quality of the book, which might even be a good entry point for many a reader.