Well, First off, make it really fun! Next, go make a dragon that kicks ass! Third, if any of those do not already help you, then make about ten different races to be for the players and give each one it's own special skill, like give thieves the ability to steal (DUH!). Anyway, what would make it really cool is if you could either go inside buildings, or you make an airship that players not only fly, but can run around inside! I would love to see a midevil game with an airship...don't know why thought!
well...make it kinda like you have options! I mean, don't make it that you have to enter a dungeon, but make it more free, like you could go around a mountain, up a river, or in a dungeon! Make millions of towns, because towns are fun! CrAzY fun!
Also, make options optional!