This is a collection of rings for Pathfinder/D&D3.*, so this review already assumes that you want one of those.

As advertised, this is 30 different magic rings, aimed primarily at defensive applications. They have a great deal of diversity and flavor, with solid mechanical descriptions of each of them. They vary from rings that project protective auras to allies, to those that deflect or absorb particular sorts of magic attacks. The mechanics are (for the most part) well integrated into the Pathfinder/D&D system, and are based on already-existing magic items. This is good because it means that the mechanics are not going to alter the balance of your game too dramatically.

An early designer's note gives the one example of mechanical deviation, but it's a bit of a doozy. The note indicates that fixed-DC magic items are difficult to balance at different character levels, and therefore these rings become more powerful as the user rises in level. This dramatically increases the power of the rings - and for casters, the increase is even more dramatic. One thing that D&D3 doesn't need is more powerful/versatile spellcasters. The drain on resources in creating level-appropriate magical rings is an important part of balancing that system. Because of this, several of the rings have costs or effects that are out of proportion. Characters at different levels are supposed to wear different rings! I have to mark it down one star for this.

The rings are indexed alphabetically, and bookmarked alphabetically, and I can't think of a better way off the top of my head to do it. A table in the front allows GMs to roll randomly for a ring, which is great, and oft-overlooked in treasure books.

So speaking generally, this is a good starting point for rings, but the mechanical changes in some of them make it so that you need to pay close attention to what you're using. Give it a go, it's a solid work, just be sure that you know what kind of mechanics you're introducing into your game.

I almost forgot, the work comes with a printer-friendly version, which has no graphics. This is a welcome addition. Weirdly the printer friendly version has no bookmarks. I would almost suggest that the printer friendly version, if it's meant to be printed for handouts, should instead focus on making item cards for the rings, so descriptions are not split between two pages.