Gamasutra - Ten Tips For Managing Difficulty In Games. By veteran developer Brett Douville.
"Lately I've been playing Buffy the Vampire Slayer on last gen's Xbox, and it has stirred up a few thoughts I have about difficulty -- mostly because it gets it so horribly wrong. I've been gaming a long time, and have come up with a long list of must-haves for most games, particularly games which target the mainstream audience."