I finally got past rank 55 in CoD4 multiplayer, which means that I've entered Prestige Mode. Prestige means that all of my weapon and Perk unlocks, and all of my Challenge completions are undone, but my stats remain intact and an icon by my name tells everyone of my accomplishment.
This is an awesome feature. Gamers have always been able to start games over, but it's rare to be rewarded for doing so (unless you count accomplishments for higher difficulty levels). CoD4's system offers only bragging rights. I'd like to see games with more tangible rewards for restarting.
Diablo 2 might have the best reset system. After completing the five-act adventure, the player has the option to replay all quests and areas while retaining all skill, attribute, and equipment progress. It's the same adventure taking place under very different circumstances -- a powerful player-character, powerful NPCs, more loot and more skills.
An MMO that never really materialized, originally called Realms of Torment, had a concept of character generations. The player's character would slowly age and eventually die. In that time, the character would marry, which would produce a child. The player would then start over as the child, but the child would begin with some of the former characters equipment and a blend of both parents attributes and skills. Theoretically, the marriages could take place in different parts of the world, thereby allowing each player-character to begin from a different location. And the cycle repeats.
Another failed MMO, Trials of Ascension (one of my favorite game ideas), also allowed characters to die permanently. But in that game, each life of the player would have tangible effects on the gameworld. And the player had the option to sacrifice some time to leave an artifact behind. The artifact would be an item with extraordinary power, and possibly an associated legend, hidden randomly in the gameworld for another player to discover.
There are many ways to reward players for starting over and keeping that replay fun. I wish games would do so more often.
Incidentally, this gives me a very general idea for a game. Imagine a single-player adventure with automatic saves and no manual saves. Throughout, there are many choices, some with far-reaching consequences. There are many possible endings to the game... not just plot possibilities, but which characters end up alive or dead, successful or defeated, etc. Each time the player beats the game, he can do it all over again with knowledge gained from experience, shaping new choices.
The gist, and the hardest part of the game's design, is to make it difficult for the player to find a wholly satisfactory ending. In other words, the player is encouraged to keep replaying until he achieves the "perfect" playthrough. If many of those choices are not as simple as right/wrong or happy/sad, then the player might sometimes change a decision and realize the first was actually better. Anyway...