As I've mentioned in other reviews of Gotham Central, the book has received near-universal praise and, frankly, I think it deserves all of it. However, this book volume is typically treated as being a step back from the best stories in the series, but even if it is, that would still make it better than 90% of comics out there. So, short review: Must Buy. Longer discussion below.
The stand alone story at the beginning takes a different approach than the rest of the books, telling the story of two corrupt cops who aren't actually involved with MCU. Some of the regular Gotham Central characters make appearances (particularly Corrigan) but it's focused on these new characters. Essentially, where Gotham Central is about the cops one step removed from Batman, this story is about the cops one step removed from them. It's an interesting story and has a pretty great pay-off.
Then there's the dead Robin story, which I particularly enjoyed. It captures a lot of what makes this series special. In fact, the story I could have really skipped was the issue that takes place during Infinite Crisis. Now, depending on how you feel about Infinite Crisis, you may enjoy the issue more than I did (aside: I thought Infinite Crisis was pretty much a mess), but it really jumps away from the tone that I enjoyed in the series.
Finally, there's the volume's namesake arc: Corrigan. This is where the book tails off in my opinion but, again, still better than almost 90% of the books out there. I can't recommend this series highly enough.