It's about a new American Civil War, set along the Red State/Blue State ideological divide. I just finished it. It's really bad; so much so that I had to make a determined effort to finish it (I have no problem not starting books, but I didn't want to abandon yet another one.)
The Real World = Walking Robot Tanks
Empire is basically set in the here and now, which is why it's particularly jarring when the 14-foot-tall bipedal tank mechs take over New York. Not to mention the later chase scene in Great Falls Park (Maryland side), featuring a PT Cruiser and rebels on rocket-armed hoverbikes.
[Since Empire stems from a video game treatment, it is perhaps not his fault, but it's still pretty wacky.]
Of course, this is only after the al Qaeda suicide scuba commandos swim up the Potomac, into the Tidal Basin and launch a rocket attack on the White House, killing the President, Vice President, Secretary of Defense, and Chairman of the Joint Chiefs.
Oh, and al Qaeda is only a pawn, used by leftist elements in the U.S. Army (?!) as a pretext for a coup by the Progressive Restoration, which is masterminded and funded by billionaire Aldo Verus (a very, very thinly-disguised George Soros), who has his own secret underground lair beneath a mountain lake -- complete with robot army.
Card: Fair and Balanced
Now, in his afterword, Card says he's a moderate, decrying extremism on both sides (he probably believes this), and at points in the book, his characters say the rebellion could just as easily been started by the Right.
But it's fairly obvious where Card stands in his fair-mindedness: All the bad guys are lefties, and all the good guys are right-wingers who watch Fox News (in fact, an appearance on the O'Reilly Factor becomes a key element), save for a few tame, pet progressives.
There's also a lot of Mary Sue-ism in the book, particularly in the early chapters, where there's a lot of unsubtle breast-beating about liberals in the media and academia, as well as throwaway cheap shots at the left and reverence for Bush from the mouths of his protagonists.
You can also see some Mary Sue-ish wish-fulfillment towards the end, where (spoiler alert) a quintessential moderate, who may or may not be pulling all the strings (including those of the Soros-arch-villain, reducing him to the ultimate useful idiot), using only the power of his ideas, becomes president by acclamation after being nominated by both the Republicans and Democrats.
Influences: You, Sir, Are No Jack Bauer
There are many shades of Card's previous works -- particularly the post-Ender's Game Shadow books (including: geniuses, evil and not, orchestrating events; family discussions that turn into graduate-level policy roundtables; a Hegemon-like President relying on a small team ["jeesh"] of hypercompetent Special Forces; portraying those soldiers with fanboy reverence; etc.)
Because it's set in the "real" world, this unmasks some of the shortcomings we'd be more inclined to forgive in the futuristic, military supergenius-soaked setting of the 100-years-from-now Shadow books -- particularly the cardboard-cutout characters and their dialog, which at times devolves to action movie buddy-banter that rings completely false.
Card, in the afterword, also credits watching 24 to help set the action-thriller "rhythms and energy," which may explain the origins of a finger-cutting scene and why they have to break both arms of a prisoner instead of, say, binding and gagging him. Though it doesn't explain why the climactic infiltration of the villain's secret underground lair is so tedious.
He also acknowledges Google Maps for the turn-by-turn descriptions of the chase scenes, which likewise end up being pretty tedious. Though we do see some references to local flavor like Hain's Point, the Borders in Tyson's Corner, and even the Rio Grande in Reston Town Center.
Moderate: You Keep Using That Word
Regarding the politics of the book -- I wouldn't mind so much if it were just a straight-out conservative rant (his characters are definitely two-dimensional enough for it -- "Orson Scott Cardboard" is admittedly juvenile name-calling, but it seems to fit here).
What I don't like is that Card keeps going on and on about how reasonable and fair-minded he is, and that he's a moderate railing against extremism on both sides, whereas it's pretty obvious that he's a right-wing conservative in denial; just because he doesn't buy into the entire traditional conservative package, or that he takes extremist positions from both sides, doesn't make him a moderate -- it just makes him a MINO: Moderate in Name Only.