As has often been noted, there are many difficulties inherent in telling a story through the IF medium, and one of the most-remarked-upon is the difficulty of keeping the player/reader involved (by giving him/her something to do) while still telling the story that the author wants to tell. The solutions usually boil down to relinquishing control of the pace of the story (typically through giving the player puzzles to solve), or avoiding/minimizing the puzzle aspect of IF and sending the player through the story with little opportunity to affect it. Emily Short's Metamorphoses doesn't, exactly, transcend this usual duality in IF design, but it does do some interesting things that help bring the poles together, and it's a wonderfully immersive playing experience.

What's going on is hard to pin down, but the heart of it is that you're a slave/servant girl sent on a quest/errand of sorts by your master, with whom you have an uneasy and complicated relationship. The literal content of the quest (to the extent that there is any) disappears as the setting changes: the game is set in a fantasy world of sorts, though it's not quite accurate to call it fantasy. The action, so to speak, lies mostly in the realm of the figurative: you're encouraged (well, I felt encouraged) to view your quest as important more in what it suggests than in what it literally depicts. By the same token, when you encounter puzzles, they have symbolic significance that goes beyond the "acquire the object" goal. (All the more so since it's not immediately obvious why you're acquiring the objects.) Since the plot goes on beneath the surface of the literal action, the game can safely permit the player to do whatever he or she wants with the pace and order of the story, since there isn't really a narrative thread as such that can be broken. For example: one puzzle requires that you give up something familiar to you to advance the story, an act which clearly has its own resonances, and another requires that you transform another familiar object and put it to a novel use. The game comments directly on some of these points but not all--very little is spelled out.

The world where all this takes place is only indirectly related to the ordinary physical world, and the relationship parallels other elements in the plot. Idealized forms play an important part: two statues of a man and a woman are described in ways that suggest Greek sculpture, and perfect solids are central to the story. Essences are important as well: virtually every object is made of a single elemental substance (wood, glass, metal, etc.), and you have the power to alter those substances in certain ways. Symmetry is everywhere (in the game's map, and elsewhere as well), and the multiplicity of mirrors suggests the reflection and introspection that are central to the plot. (Likewise, the idealized forms suggest the absolutes that make up the plot.) At the same time, the game's world is sterile, arid: there's nothing particularly warm or welcoming about it, and there's no suggestion that you find it pleasant or comfortable. (Left ambiguous is whether the dryness reflects the protagonist's life as it has been, or represents some hostile reality external to her that she's trying to overcome.) The setting itself tells a story, in other words, in a way not often found in IF.

Not only does the setting play a part in the plot, however, but it's also beautifully described, with plenty of arresting imagery--some descriptive, others suggestive. For instance: 

Dome of Broken Light
A straight white light comes through the hole in the ceiling, but it is soon
after twisted and bent: mirrors cast it from angle to angle; crystal divides
it; glass stains it.
The picture is indeterminate: the reader is encouraged to imagine a riot of reflections and refractions. The only perfection here is that of perfect confusion. Here, by contrast. 
Glass Grove
An orchard of glass trees: trunks slender and orderly as the columns of the
Alhambra, foliage iridescent and frail.  No wind stirs, and yet, from time
to time, a leaf casts free of its branch and drifts to the ground.  The whole
floor of the cavern is deep with them.
.the image is more concrete: "iridescent and frail" conveys both the beauty and the sterility of the game's world. The writing also underscores the contrasts between the two locations: the (relative) activity of the first is reflected by the active verbs ("mirrors cast," "crystal divides," "glass stains"), whereas the aridity of the second is suggested by the intransitive verbs ("casts free," "drifts", "is deep"--and the first sentence has no verbs at all). Most of the writing is spare, like the game itself--you eventually learn some things about yourself, your past, and how you came to be in your present position, but the snippets are small indeed. What's there, however, is well worth reading.

Metamorphoses does an impressively nuanced job of worldbuilding, in short, but what's noteworthy is that the gameplay is nearly as good. The puzzles feel reasonably novel, due mostly to the transmutation/magnification machines you're given and which figure in all the puzzles. The technical aspect is impressive--the objects by and large do what they're supposed to do when transmuted or enlarged or shrunk, and they interact with each other in plausible ways, nothing to sneeze at considering the complexity involved. Moreover, there are plenty of multiple solutions that draw on the various qualities of the objects whose size and essence you can alter, which makes the puzzles flow by fairly quickly. (This is not, in other words, a "guess what the author's thinking" sort of game, at least not when it comes to puzzle solutions.) Not every object in every state and size gets a customized description, of course, but everything behaves sensibly enough.

Metamorphoses is not a flawless effort--some of its design choices risk leaving the player cold in certain respects. In particular, the game leaves so much about the protagonist ambiguous for so long that it's difficult to connect to her emotionally. Some of the most emotional experiences for the protagonist come early enough in the story that the player is unlikely to be as strongly affected as he or she might be with some more setup and explanation. As always, the tradeoff between story and puzzle raises the possibility that the player will forget about the story amid all the mechanical fiddling (particularly here, where there's so much fiddling to do)--the puzzles are reasonably well integrated into the story, for the most part, but most of the plot is sufficiently abstract that it's easy to lose sight of what's supposed to be going on. Finally, and perhaps most importantly, there are a lot of endings to Metamorphoses, and many of them don't provide much resolution in any obvious way; finding an end to the story that adequately brings the various threads together may take a while for some players. In a way, that works here; it reflects the general bleakness of the game's world that the end of the story doesn't tie up all the loose ends or furnish an especially satisfying conclusion. The game aspect, however, demands some sort of conclusion, whether optimal or not, and only a few of the endings offer real conclusions as such.

These drawbacks are to some extent inherent in what Metamorphoses appears to be trying to do, though; tastes on what constitutes a satisfying game experience differ--and the latitude for experimentation provided by the machines helps make up for any other problems. For my part, the setting itself was enough to make this the only 10 of this year's competition (and the only one I've given since 1997)--as worldbuilding, this is a triumph.