It's easy to think of Uru Ages as "more Myst", but the adventure game has become a much broader idea. Also, many (most) kinds of games these days include adventure *elements*. All of these disparate directions can serve as inspiration for Uru Ages.
So what kinds of Ages has Cyan never given us?
(If that sounds arrogant, remember that in the past eight months Cyan has given us several kinds of Ages that are new to the Myst universe. Cooperation in small groups, cooperation in large groups, the toybox... And the older Uru Ages were equally experimental. The GZ marker hunts, the timed puzzles in POTS, etc.)
My random thoughts:
- Nightmares. (There are several good independent horror adventure games out there.) The Age conveys looming dread to the player. Claustrophobia, disorientation.
- Reactive environment. Every step causes a chain reaction of light, or sound, or motion.
- Portrait. An Age which reveals a history, or story, unrelated to the D'ni. (Remember that a newly-written Age can have a population and a history.) The player discovers the story as he explores.
(footnote: Tragedies? Triumphs? A wasteland, in which you discover how it spiralled into ruin?)
- Customizable playground. The player can adjust the Age, with in-game controls, to suit his desires. (Okay, Jalak already does this, in a small way. As does Relto. But there's a lot of room for expansion.)
- Workshop. A set of tools, which can be cranked over time to produce some kind of product. (Like the Ercana ovens, but with a direct -- if slow -- effect in the Age itself.) For added fun, have several machines which must be cranked simultaneously for efficient production.
(footnote: "workshop" is too narrow an image. "Cranking the machine" could just as well be gathering herbs.)
- Abstract visual world. The Age conveys a purely artistic effect, rather than a (para-)realistic one.
- Governance. You survey a tiny garden, or process, or civilization, and influence its growth with various tools.
- Combinatoric garden: Many different elements, in constant change. Some slow, some fast. The elements interact in interesting ways. You can sit and watch, and no combination will repeat -- not for weeks, anyway.
(footnote: Could do this with sound as well as with visuals.)
- Dream world. The Age conveys something in metaphor, subconscious imagery, and dream-logic. (Again, not a realistic environment.)
- Tight visual focus. What if you could only see a few feet? How do you absorb that environment? (Tetsonot does this, but it has no surprises in its layout.) Fog, darkness, even blinding light.
- Collapsing environment. You knock down walls, topple constructions, break ropes in order to proceed through the Age. When you reach the end, it's a ruin. (Deliberately no replay value -- if you want to see it again, reset the book.)
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Feel free to add to the list. Warning: also feel free to say "But that sort of Age shouldn't be in Myst!". But I'll just smile and nod and then maybe go do it anyway.