This book is excellent. It's exactly what I needed for my currently urban (Bard's Gate) focused campaign. 25 two-page lairs including brief hooks, maps, short room descriptions and monster stats.
Extremely usable. I play with Swords & Wizardry (OD&D) rather than ACKS and the stats are pretty much identical. It'll work perfectly with Labyrinth Lord, BFRPG, AD&D, whatever. OSR stats really are interchangeable so don't let the fact that it says ACKS put you off.
I'd happily buy a 2nd release in a line of Urban Encounters.