Pagan Shore is a Pendragon supplement which describes Ireland as it might have been in the Arthurian era. It's a way for us to experience a culture that has little connection to today, unlike Arthur's Britain.
After a brief glossary which explains some of the social structure of the various cultures who lived in Ireland, there's a listing of hundreds of places of interest (including a few in Britain), and maps showing geographical features and political units. The loose 11*17 inch map includes even more interesting names which a GM could use to spark an adventure.
History is compressed so that five cultures live simultaneously in Ireland: the Cruithni (Picts), the Erainn (usually Pagan Celts), Gaels (usually Christian and somewhat more politically cohesive Celts), Lochlannach (Vikings), Feudal Irish (promising students of Arthurian culture), and the British invaders.
Magic extends the 4th edition rules to derive Life Force from directions (e.g. travelling widdershins), bardic skills, and sovereignty. There are new magical effects, and descriptions of druids, poets, and monks. Many Faerie creatures have game statistics, and the many deities are touched on. Finally, there's a section on geases, taboos which druids impose on people in an attempt to avert various dooms.
Character creation allows for magicians, and introduces foster families. Ireland is especially suited for women characters -- not only is there a herald profession reserved for women, but the epics mention women warriors. There are new rules for chariots and slings, and revised passions.
The brief section on storytelling describes Feats, and has five short adventures. Finally, there's a character sheet for tribal Irish characters.
The writing is clear and concise, and low in gaming terms. I found the linguistic approach (describing the origin or meaning of many of the names) useful, and learned how many fairy tales are based on Irish law. Pagan Shore inspired me to read some of the Irish epics it's based on, and made them much easier to understand (likewise, they helped illuminate Pagan Shore). It does a good job of making the tales playable, while wisely leaving out some of the extravagant trappings (like five-pointed spears or Cuchulainn's warp-spasm).
Pagan Shore takes advantage of the Erainn family structure by making all Irish characters eligible for election to chieftainship. Some characters may prefer safer goals, such as becoming a professional poet or judge, or a future saint, or they can simply concentrate on gaining wealth (measured in cows) or taking trophy heads. The possibility of playing a Viking trader further expands the character roles. All of this fits well into the Pendragon rules, with only a few specialized additions necessary.
The background is largely self-contained -- gamemasters would need to refer to Pendragon for the rules, but could ignore its cultural details and have a simpler setting for adventures.
Like many Chaosium products, Pagan Shore suffers from its lack of an index. Historical information is found in any chapter, and can be hard to track down. It's hard to locate a point of interest since there are no map grid references. Many people will find the extensive use of Irish terminology confusing (and hard to pronounce, though that's not the author's fault). And while the cover is striking, it features a woman warrior wearing bikini-like armor that doesn't seem to fit the culture, and annoyed my wife. (The interior art shows only normally-clad women, and has a naked male warrior.)
Pagan Shore is perfect for extending Pendragon to roles besides knights (and magicians). I found it a well-written introduction to a interesting culture that's highly suited for gaming. After reading it, I wanted to start an Ireland-based campaign. If you're already running a British campaign, it's a great source of lands to ally with or try to conquer.
Fans of Glorantha will also find Pagan Shore useful, since many of the Irish (and Viking) customs (e.g. the loose tribal organization with king elections) are similar to those of the Orlanthi tribes.