Tetraform, the new game from Tyler Glaiel and Greg Wohlwend, casts you in the role of planetary defender, and combines space combat, yo-yo physics, and elements of the Grow games to do it. In the center of your screen is your pretty polyhedral world. Waves of enemies come in from the sides of the screen, all prepared to crash into your fragile little planet. The only way to stop them is to click on two of them, causing them to become irresistibly attracted to one another, resulting in their eventual spectacular collision. These collisions net you points and also rain resources down on your little planet.
As the game progresses, you'll deal with larger and smaller ships, each of which have their own specific gravity or abilities, including being able to shoot missiles or phase into two identical copies, only one of which is real. You'll also learn to turn enemies' weapons against them, and snare multiple enemies into collisions that cause larger explosions and net more points. Sometimes when waves end, you'll have a chance to pick up health power-ups, as well as procure some power-ups that appear as structural additions to your planet, but be careful, as waves will start quickly one after another, so be speedy about getting your goodies.
Analysis: Tetraform's biggest asset is definitely its clever gameplay. The attraction/gravity mechanic, while reminiscent of a couple of other games, feels exciting and well thought-out, and having to plan which ships to crash into one another manages to be both strategically satisfying and explosively fun. The game suffers, however, from the lack of a tutorial, as there are mechanics and ideas that don't seem well explained. What, for example, are the plates of dirt and grass that appear on your planet? The game is called Tetraform, which seems to indicate that terraforming the planet is some kind of goal, but it's never clear how you're supposed to reach it, or whether making grass grow on your planet is part of that goal.
That being said, the rest of the game is really smoothly executed. A variety of enemy types force you to constantly reconsider your strategy, and while the difficulty of the first couple of waves is pretty reasonable, the game quickly gets hectic when smaller crafts zip around your planet like water circling a drain. Learning how to send larger ships careening into swathes of smaller ships is one of the great moments of the game, and even figuring out how to use your power-ups can be fun, if a little baffling. The thing that originally looked like some kind of sun/solar power collector turned out to be a morning-star to run ships into, and you can click twice on the radioactive scaffolding to destroy everything on screen, which is crucial when things start getting really frantic.
If anything, the difficulty ramps a little too fast, but fortunately you can always simply continue the game any time you die (though your score gets reset,) so you'll even be able to pass the (long, fun) boss-fight with a little bit of patience.
In general, this is an exciting game with an inventive and well-executed mechanic. The simplicity of the gameplay means that the lack of tutorial isn't too much of a problem, and the music is really catchy. Take it out for a spin!