I'm very satisfied with the quality of this product. It delivers just what it promises—foes for fledgling heroes—and goes beyond that in the degree to which each NPC is interesting and engaging.
Every one of the 12 unique villains it contains includes a well-written and creative background—the characters really come to life. Each NPC includes a goal and plot section, which makes it easy to drop any one of them into your campaign with minimal effort. And, since they each include a tactics section, they're easy to run once combat starts, too.
The background profile in soft blue on the cover is very attractive, and the style of the interior art is great. Those of you that favor an old-school style will particularly like the character drawings.
The layout is slick, and understated, and nothing jumps out me as difficult to find or read (the NPCs appear in the order of their CR). One benefit of the slick layout is that each page looks good when printed—without consuming a lot of ink.
The attention to detail is quite good throughout. After reading through the whole PDF, I only noticed only one minor error in a statblock (an omitted line entry), and that's not enough for it to lose a star.