I find myself amazed that this has so few votes. It's a phenomenally in-depth sailing game that has multiple overlapping playstyles. The turn-based ship combat was amazing, the sense of discovery was fantastic and it has one of the most addictive and evocative trading systems of any game I have ever played. Sailing across the world passing on goods and moving the markets.
There was something about upgrading from a hold full of carpet to cinnamon, cloves and porcelain that was simply fantastic. Each character has a story to progress through but I found it impossible not to fall into the sandbox and just roleplay my own story!