Gluttony, on the whole, is not really a sin that motivates player characters very much; it's more something that they face, from creatures such as rust monsters and oozes. This, then, is the major theme of this supplement, and it has somewhat mixed success.
As with the other books in the series, this has 6 pages of content, with good artwork, and only a few minor proofing errors. One page is taken up with a general discussion of the sin, and a short template to apply to gluttonous monsters, and half a page with a (rather limp) cautionary tale set in the Free City of Zobeck.
There are, as always, four monsters, described in about as much detail as a typical Monster Manual entry. They range from CR 5 to 18, and some of them are better than others. The CR5 monster is a good example of a gluttonous creature, whose power is basically linked to digestion of its foes.
The next two are, to my mind, less effective. One is an attempt to use a character's gluttony against them, which it makes a brave attempt at, but ends up making the creature completely harmless to anyone who knows what it is - definitely a one-shot monster, then. Even then, the PC's gluttony isn't likely to really be what gets him in trouble (this is the issue with it not being a motivation for most characters). There's also a construct, whose link to gluttony, given that it doesn't eat, is tenuous at best - you could equally well describe it as being connected with wrath, without having to change anything about it.
These two creatures, are, however, redeemed by the CR18 ooze. By the standards of such things, it has a quite a range of relevant abilities, making it far more interesting than your regular ooze, and the link to unthinking gluttony is unmistakable. All oozes mindlessly digest stuff, but this one really draws power from that, making it an interesting challenge, as it grows to become powerful enough to consume an entire village.