Once upon a time, the arrival of a new id Software game was like staring into the future. These guys invented the first-person shooter, instituted shareware, legitimised mature content, brought us the first real 3D worlds, and obliged the industry to embrace graphics acceleration against its conservative instincts, catapulting in-game visuals forward by a generation. Every game offered a revolutionary breakthrough that fundamentally altered your expectations forever.
These days, you just don't get individual games pushing things forward like that. Instead you get shared gradual progress across a number of releases, so we see experience systems evolving in RPGs before they break into other genres and eventually help Call of Duty to conquer the world online, and everyone stands on each other's shoulders and learns together. The difference with classic id Software games was that we didn't get to see all that working in-between - you'd just wake up one morning and someone had invented deathmatch.
Now that games have been disarmed of their ability to change the world overnight, then, Rage may be the first id Software title to be judged purely on the merits of game design and content, and in many respects it more than meets the challenge.