First things first: if you're picking this up because you're hoping that the included novella, _Aftermath_, will answer the huge cliffhanger at the end of
Changes: it doesn't, not clearly. No big answers here (though many of the stories, including Aftermath, will include plenty of small details to please and tease dedicated fans).
Instead, this collection is a set of alternate perspectives: stories from the viewpoint of Thomas or Murphy, a story that shows us Harry when he was just starting out as a detective, a story that focuses on Harry when he's *not* working on a case and just trying to take a day off, a story that focuses on the Carpenter family, so forth. Butcher includes a paragraph or two of commentary at the head of each story, so we get to find out what *his* perspective is on each of the stories, too. A fair number of them were initially written for theme anthologies, so there's a certain amount of "Harry Dresden Does a Wedding Story" or "Harry Dresden Does a Birthday Story" going on, but each stands on its own merits, and fans of the series will be very satisfied with what they get here (as long as they aren't looking for answers to major plot arcs).
In fact, I'd go so far as to call this a "must read" for dedicated fans of the Dresden books: not only does each story have plenty of the action, comedy, and "Crowning Moments of Awesome" that have made the series so successful to date, but dedicated fans will find answers too all kinds of minor side puzzles that Butcher hasn't necessarily addressed head-on in the novels (like more information about Gard's true nature). That said, if you've read all the other stories in here already and are picking this up just for _Aftermath_ because you want answers to what happened after _Changes_, you won't get clear ones; _Aftermath_ is told from Murphy's perspective, not Harry's, and it's more about how Murphy personally processes the, well, aftermath of the events in that book. While we do get a few more pieces of the puzzle, it looks like we'll have to wait for the next full novel,
Ghost Story, before we see the whole picture.
I would not recommend this anthology as a starting place for new readers to the series; instead, start with either
Storm Front, the first full novel, or
Welcome to the Jungle, a graphic novel set before the events of Storm Front. Reading this collection first would spoil pretty much every major surprise in the series to date, so yeah, don't do that.
Alternatively, you could pick this collection up and then flip back and forth between it and the novels, reading in proper sequence. If you want to do that, here's a list of the stories in this volume, in chronological order:
A Restoration of Faith...(before the first book, Storm Front)
Vignette.......................Between Death Masks (5) and Blood Rites (6)
Something Borrowed.......Between Dead Beat (7) and Proven Guilty (8)
It's My Birthday, Too.....Between White Knight (9) and Small Favor (10)
Heorot..........................Between White Knight (9) and Small Favor (10)
Day Off.........................Between Small Favor (10) and Turn Coat (11)
Backup..........................Between Small Favor (10) and Turn Coat (11)
The Warrior...................Between Small Favor (10) and Turn Coat (11)
Last Call.....................Between Small Favor (10) and Turn Coat (11)
Love Hurts....................Between Small Favor (10) and Turn Coat (11)
Aftermath.....................After Changes