Curves aren't just for difficulty

"Difficulty curve" or "learning curve" are fairly common terms, but you don't often hear of similar terms related to story and theme. This is something I learned from playing Silent Hill 4, and is loosely related to my Advancement/Involvement post:

If your game can't get by on advancement alone, it had better have damned good involvement. When it comes to the story aspect of involvement, accessibility - what you might think of as the "story curve" - is a major factor. Silent Hill 1 was incredibly deep and complex, but it started out very simple: Your character crashed a car and his daughter ran off, and he has to go find her. This kind of thing is something that almost anyone can related to and identify with, and it gets you involved in the story. Only after it's established something you can really relate to does it start to twist and warp the story, but it keeps that basic drive throughout the game.

SH4, on the other hand, kind of just dropped you in a room, and immediately has a complex and inaccessible plot. The game relies on a lot of "what was that all about?" plot devices, and doesn't really have an overall accessible storyline, apart from "I am really sick of this room and want to leave."

Stories should be accessible, in a situation the player can imagine themselves in as the protagonist. The more involved the player is in your story, the better. Don't just throw them into a situation and expect them to relate to it.

Characters need to be believable and flawed, too, but that's an entirely different post.