I would post this over at the campaign blog, but since that's meant to be kept in-character, I'll post it here: my design rules for my Legend of the Five Rings campaign.
1. No conspiracies. The death of the characters' father is less tragic if it turns out it was all part of some grand villain's evil scheme. There is no hidden mastermind, and no central evil villain. Any sinister plots that show up in the storyline will have to stay away from the characters' personal lives.
2. Avoid simple dualism. Whenever moral dilemmas come up, they need to be more complex than good versus evil. The players should be forced to make tough decisions rather than having one right path.
3. Keep things open-ended. Rather than being a linear plot, there should be multiple choices to make at each stage of the game. To keep things from being too freeform, many of those choices will have to be somewhat binary, but, as above, not in a good versus evil sense. The game starts out being node-based, traveling from place to place on a well-defined map, and getting involved in local plots or accepting jobs on an optional basis, but as the central plot becomes more clearly defined, there should be a definite story arc and ending for it. There should not be one set ending, though.
4. Actions should have consequences. The choices that the characters make should shape the game world, and even tiny events should have effects that can be revisited later.
5. Avoid high fantasy. Although magic is tough to avoid, with a priest in the party, it should be played as fairly "realistic," for example, having to actually pray to the kami and keep good relations with them in order to cast spells rather than simply fire off spells whenever you feel like it. If gods appear, they should be in the form of dreams, omens, or abstract visions. Monsters should be rare and not particularly flashy and magical. Definitely no ancient prophecies, at least, not true ones.
6. No annoying allies. All friendly NPCs should be useful or at least charming, and not place undue demands on the players without doing something for them in return.
7. Honor should be important. Since some of the player characters probably want to maintain a high Honor rank, and they're forced to live as scruffy, pragmatic ronin, keeping that high Honor rank should be a challenge, making players choose between being successful and being honorable.