First up, we've got Osmos, by Hemisphere Games. You play as a sphere of indeterminate matter/energy, free floating in a bounded space. When you reach a boundary, you bounce off of it, as do all the other "motes" that share the space with you. The goal of each level is to grow in size by absorbing smaller motes by simply colliding with them. Conversely, by colliding with larger motes, your mass will be reduced, and prolonged reduction will destroy you.

You move around the space by ejecting bits of yourself in an action/reaction process. Clicking the mouse button will fire off ejecta in that direction, which propels you in the opposite direction. These pieces of yourself will bounce around the area and be reabsorbed by whatever motes with which they collide, including yourself. Holding down the mouse button will fire them off more quickly, which makes you move faster, but at the risk of losing much more of your mass, which makes you vulnerable to larger motes. As you grow larger, it requires more effort to propel yourself, as the laws of physics dictate.

You can use the mousewheel to zoom out and in, which can give you a better picture of the playfield, and the ever-shifting locations of your targets. It's important to be aware of the changing trajectories of each mote as they travel around, as it's easy to become blindsided by a larger mote and lose mass.

You can also right-click to slow down time, which might make it easier to plot your course around the playfield. On an interesting note: you may replay a level any number of times, or restart a level if you've failed it. When you do, the initial starting point and vectors and velocities of each mote is the same. So if you're having trouble with a particular level, you can memorize the way everything moves and plan your attack accordingly.

Later levels feature orbits that keep you moving in relation to a larger mass, and a "biophobe" that consumes motes, yet flees from you, requiring aggressive tactics and careful husbanding of your mass to succeed in running it down.

Osmos is a challenging, deceptively difficult puzzler that will have you seeing spots -- but in a good way.