For a year in game time, the squishy critters in World of Goo are the objects of your care, your hopes and your grief; you won't soon forget them. They fall in droves from above, spill from the mouths of stony-faced creatures, bob and splash in pools of water, and sleep peacefully in piles until you excitedly stir them.

Where are they going?

As their unseen, guiding hand, you then take your pick of the goo balls and build them into improbable latticed structures that the others traverse. They're usually headed for a hard steel pipe that whisks them away like a vacuum cleaner -- it's unclear why. The pipe creeps into the picture from one of its outer edges, its ultimate source just out of sight. And its industrial-strength sucking makes its opening highly desirable. In most of the game's 48 levels you're given a quota of goo balls to collect in the pipe. Grab enough goo and you get to move on.

But the real star of World of Goo isn't the goo. It's not the Sign Painter, either, whose wry, omniscient and sometimes unreliable narration left for you on signs littered throughout the game world is -- after GLaDOS' game-changing performance in Portal -- almost to be expected. No; the real star of World of Goo is the vivid, living world, which commands love, hate and many emotions in between.

The goo play out a constant contract with nature. You're always conscious of the strong wind that blows through the game's grassy fields; it makes the structures you assemble with the goo sway back and forth, and threatens to blow your tower of goo into a ravine. In your quest to guard the goo, the push-and-pull between you and the world -- with the goo caught in between -- never ends.

It isn't hard to feel like the world is messing with you.

This is because the goo balls are very physical beings, and as such obey the basic laws of physics. They have mass, and the world will pull them down. To keep them upright, you place them at optimal load-bearing angles. If not adequately supported, they fall victim to one of the world's many threats -- a chasm, pool of water, bed of spikes or fiery pit. In the game's most precarious moments, you'll need to learn how to mitigate or manipulate a moving goo structure's inherent momentum. In its most rewarding moments, the structure stays safe.

It's usually possible to grab much more goo than the minimum quota, so the real challenge (and replay value) of the game lies in figuring out how to use the least amount of goo to build a structure that will save the most. But it's the first playthrough -- the first few showdowns with the wind -- that wins you over.

Often it isn't apparent what shape of goo will conquer a given level's dangers. But the world patiently teaches you how to interact with it, if only by gently demolishing each new structure you come up with. It's not long before you have a good intuition for the amount of reinforcement that's needed for a bridge, what length of dangling goo the wind will blow safely over a razor-sharp windmill, or how you can simply let a giant goo ball fall to safety.

You have to burn the ? goo.

The goo aren't all inky black. Green goo can be placed and later pulled back apart to change the shape of a structure. Red goo explodes when lit by fire. Pink goo becomes a balloon that can lift the other goo. Lipstick-wearing goo needs to be looked after. You meet new species of goo every few levels, and it's a delight to see how they behave with each other.

Because the goo is realistically gooey, and for all your Newtonian know-how, the structures you create shiver fitfully as they hover above uncertain doom; you aim like hell for that vacuum pipe, and thumb your nose at nature. The pipe literally sucks the goo lattice into shape as soon as it's close enough -- thus erasing any imprecision or outright flaws in your construct with raw machine power.

World of Goo's own shortcomings are few, but they can grate. The goo can be hard to pin down. For instance, you may find yourself burdened with a small goo lattice that is about to fall onto a spiky, churning wheel. If only you could quickly enough dig through the 40-odd goo balls crammed onto its surface to grab the one goo balloon that could lift it out of danger's reach. For a game with clear puzzle roots, World of Goo relies a bit strangely at times on reflexes and click-and-drag timing. You might wish you had a real controller, or at least keyboard shortcuts for toggling different goo types.

You get blown around a lot in Chapter 2. Each nub is a level.

There are "time bugs" that float around and can be used to rewind your mistakes, but they are limited, and can sometimes -- of course -- be set off by accident, as they innocently flit in front of the burgeoning, swaying goo structure you are frantically building. In those brief moments, you wonder what exactly made you so committed to becoming the goo's caretaker.

And the omnipresent Sign Painter's messages, which not-so-subtly hint at how you might bypass the dangers ahead, make for a very thin, gratuitous layer of narrative -- a red herring. The signs are mostly a space through which the game-makers' voice can shine, though they should've stopped at heaps of bubbly, colorful goo. The Sign Painter's words are smug at best, exasperatingly righteous at worst. We get it; mega-companies, even ones that make games, can be dehumanizing; and maybe it's the little people -- the goo; 2D Boy; yourself -- with whom our future resides. True, but they had me at "summer."

That's the season when World of Goo starts -- when you fall in love with it -- before it dips into an ominous autumn, a very harsh winter and a long-awaited spring. In the summer, life with goo is all rolling green hills. The wind that blows everywhere in the fields not only bullies your goo; it also powerfully conveys the exhilarating effect of being out in the wide open.

This may be the most fingers you'll ever see in the game.

Later, the world feels a little darker and a touch sadder. You catch isolated glimpses of it in each new level, but you're barred from exploring, so you try to funnel the goo into the pipe as quickly as you can just to get the next glimpse. You enter spaces that are absolutely still -- wintry caves cut by shards of light, valleys bathed in sunset, great swamps. There, you catch your breath after the race against the wind, and refocus on the goo at hand.

Finally, the world gets meaner. You guide the goo through massive tunnels and water-filled pipes. You build towers amidst power lines that are buffeted by wind and rain. You scrape through the insides of coarse, smoky furnaces. Late in the game, you delve into another world that has an altogether uncanny spark.

You stick with the goo through all of these nearly tangible dangers, and this is why World of Goo is surprisingly moving. More than a cute, squishy romp, it's a long, tumultuous dance with nature. In the game's difficult three-level coda, you're taken to islands high in the sky, where your opponent is -- once again -- the wind, stronger than ever. By now you're happy for the extra challenge. You've scrambled through thick and thin to get up here, and you want to take your time to say goodbye.

This review is based on a downloadable copy of the game purchased by Crispy Gamer.