Of course...of course Andy Diggle left Action Comics after only one issue...
Because there is no sarcasm expression in written form (yet), I'll make it clear: DC editorial is letting some of their BEST talent walk out.
Action Comics #19 is a great issue. Seriously; after Grant Morrison's 18 issues of crazy, Andy Diggle gives readers a story that's incredibly interesting without having to unwrinkle your brain afterwards. It's Superman battling giant alien monsters. And the best characterization of Lex Luthor I've seen so far in the 'New 52'.
This is supposed to be the flagship Superman title (until Superman Unchained, of course), and keeping Diggle would have been in DC's best interests because this man knows how to write the Man of Steel. Morrison stretched Superman to limits we've never seen before, and now Diggle is bringing him back to reality a little bit. Besides Action Comics, the only other solo book is Superman, which Scott Lobdell has driven into the ground. If you're looking for straightforward Superman action, Andy Diggle's Action Comics is for you. Action Comics #19 balances Clark's life as a reporter (and human) against his life as Superman more organically and smoothly than any issue of Superman or Action Comics before it. Diggle understands the need for this balance and he approaches it with a "less is more" attitude that simply works.
UNFORTUNATELY, Diggle is yet another casualty in DC's iron-fisted editorial rampage. It seems that unless you are Grant Morrison, Geoff Johns, Scott Snyder, or Jeff Lemire, DC is going to edit the every-loving hell out of your work to the point that you'll want to no longer be associated with said work. So all we get is this singular issue from Diggle. Arc artist Tony S. Daniel will be taking over scripting duties from Diggle's plotting, but it's not going to be the same because Daniel is not as strong a writer as Diggle.
Action Comics #19 shows such great promise from such a fantastic writer that it's hard not to think about Andy Diggle's problems with DC editorial while reading. First, his timeframe was pushed back a whole month to accomodate Grant Morrison's desire for an extra issue, then he was given the "WTF" directive (something many DC writers had to contend with by shoehorning a 'major revelation' into their stories) that became his first issue for the title, then he and editorial butted heads even further which caused his departure from the title.
In the end, all we can do is appreciate Action Comics #19 for what it has become: a sign of amazing potential that won't be fulfilled.