Well, the talk on difficulty in games keeps coming โ€” Gamasutra has an interesting essay up that's a slightly different take on the problem of challenging players while not making the game inaccessible to everyone but the patient, dedicated hardcore contingent. Designer Daniel Boutros examines a number of ways in which games have tackled the difficulty question, and what games have done it well. Save/checkpoint issues also come up:

The truth is, wider checkpointing tests patience and memory as much as it does skill, which can frustrate and put off players. Call of Duty 2 had the best checkpointing implementation I experienced in the new generation, which was expanded even further with Call of Duty 4. Not only was each intensely exhilarating section in veteran mode beatable within 5-10 minutes (in Call of Duty 2, specifically), players would also get save-able checkpoints which appear before and after a cut-scene, saving players from classic tedium moments such as the "Look at all dat juice" scene from Gears of War. This infamous portion of Gears of War placed players against a group of the tough Theron Guard enemies as they laid siege to a pumping station. Dying in battle restarted the player a long walk back before the action began, replaying a verbal scene in which one of the characters utters the immortal line, "Look at all dat juice." Repeating this became annoying after a while.

It's a nice, non-whiny take on the difficulty of designing for difficulty, and some solutions that have panned out well for designers and players alike. Difficulty is Difficult: Designing for Hard Modes in Games [Gamasutra]