Dungeons and Dragons is a game containing many games. The very nature of the game shifts as player characters become more powerful and more capable. Things that challenge or stonewall — perhaps literally! — low-level PCs become mere nuisances or even decorative elements at higher levels. The chasm that was a nigh-insurmountable obstacle at one point becomes a trivial obstacle or source of curiosity.
Echelon develops this further. There are explicitly five tiers of PC ability. At the base are veteran characters, more capable and durable than the general populace. Then come larger than life heroes, superhuman champions, paragons who epitomize all that they are… and the legends stand far above them.
Characters no longer have classes. Instead, a character has talents that together define the character’s abilities. Each talent can grow as the character advances, granting more and better abilities the more capable the character becomes.