Talk about a downer. Not even the Age of Apocalypse (which wasn't exactly cheery) carried the weight of despair that Age of Ultron lives under. In AoA you at least got a sense that these characters were still fighting back. Not here Sam (not sure who Sam is, just felt like saying it). Everyone is in pure survival mode, and it seems that our heroes are in as much shock about what has happened as the readers are, and that doesn't bode well.
In a recent interview writer Brian Michael Bendis said Age of Ultron is less concerned with how it happened then what happens now, and he definitely delivers on that promise in issue 1. No real insight is given as to how Ultron came to power so quickly, but from the looks of it whatever did happen seems to have taken the fight out of everyone, at least except Hawkeye. The man with the arrows gets a huge spotlight here, and shows exactly why he is an Avenger (not that anyone was questioning that of course, but reminders are always good).
The action is beautifully illustrated by Bryan Hitch, giving an immense sense of scale (Ultron's floating city/ship hovers over what's left of New York) and conveying just how bad things really are. Hitch's style fits the book perfectly, and while he won't be illustrating the whole series (just the first five issues), I'm looking forward to seeing more from him.
As for the writing Bendis shows just how tense things are amongst the heroes that are left, and gives some subtle hints about where certain characters are and how things got here, but again, it isn't the focus. You won't find any huge pages of exposition here on "well this is how it all went wrong". The most telling piece of dialogue comes from Hawkeye, and I think it sums up this issue best.
And I'm not going to let what happened change the value of MY life.
And SHAME on the rest of you,
Shame on you for GIVING UP.
I can't remember a story where these characters looked more defeated, perfectly illustrated on the last page.
We've seen them at their lowest, now let's see if they can get back up.