One thing I've always found to be a difficulty in an RPG set in "modern" times is that the players are too familiar with the way things work in the real world. If you throw together a medieval roadside inn and map it out, only the most hardcore dorks are going to nit-pick. However, if the secret lab your PCs are storming has no restrooms indicated on the map, somebody is going to notice. This problem extends to other areas of the game as well, but that's a different review.
Critical Locations is 63 pages of maps and useful information to go with them, like occupants (that is, NPCs), Structural Features (like the stats on doors and walls and vending machines the PCs might want to break), and the always popular, adventure seeds. Each location also has specific information related to it, like rules for trying to check into the "Roadside Motel" anonymously, or what happens when people start trying to stampede out of the movie theater at the "Cineplex".
The book features 29 different locations, mostly urban settings, each with full color maps marked with d20 standard 5 foot squares.
Overall, the book does what it sets out to do, and does it well.
However, despite the fact that I find the book to be very useful, I'm not sure I'd ever buy it at the cover price. I might, but it would be the subject of quite the internal debate first. The book, while a useful tool, is certainly not necessary.
Thus, if the price doesn't bother you, and there's nothing else out there that you feel the need to by right away, I'd recommend it.
d20 Modern Critical Locations
Publisher: Wizards of the Coast
Format: 63 page softcover
Price: $19.95 US
ISBN10: 0-7869-3914-1