5 out of 5 rating for Waterlands: Adventures in the Great Mire
Waterlands is best used with the Mythic Britain campaign book, the big adventure does stand on its own outside of the Mythic Britain campaign. You will need the character generation guidance to make appropriate PCs as it's slightly different from core Mythras, although you could wing it at a pinch. Druids in the setting are quite different from standard animists of Mythras, and also have extensive setting specific rules and guidance in Mythic Britain.
Waterlands is largely self-contained and distinctively it's own little corner of the Mythic Britain world - the fenland setting is used to full effect, it's got region-specific encounters, natural and supernatural creatures appropriate for the marshy terrain, environmental hazards, colourful and important NPCs are detailed, a short but varied adventure (travel, social interaction, a mystery, mayhem, the supernatural, an Old Man who may be Merlin or ... Tim) and enough additional adventure cameos to make a campaign of it. Very flavourful of Mythras' take on Dark Ages Britain.
This is a brilliant format for a short supplement.