Osmos is called a "casual," "ambient" game, but I'm here to tell you IT IS NOT! Osmos is nail-bitingly suspenseful and brutally difficult! It reminds me of Lunar Lander, requiring precise movements to succeed and no room for just gunning it, or pushing your way through obstacles!
The dynamic around which the game is based is incredibly potent. You are a primitive, single-celled life form. Your goal is to gain mass and survive. To gain mass, you must absorb other creatures. But to do that, you have to be more massive than they are. But to move around to absorb others, you have to give up mass. It's a beautiful paper-rock-scissors love triangle of death. You can't just barge around. You must strategize, plan, drift, take your time. Restraining yourself takes effort.
When you start out each level, just about everyone is bigger than you, and a single touch from them will kill you! It's a perfect metaphor for life itself: the only way to get bigger is to gobble up everyone who is smaller than you. Once you reach a certain size, nothing can stop you from absorbing it all, and reaching this point is the most satisfying feeling in the world!
A very well-made gaming experience. My only complaint would be the final couple of levels. They're damn near impossible and totally out of place. All of a sudden it goes from a game about biological life to something that resembles plotting Voyager 1's route? What the hell...? Challenging, yes, but wow it's out of place.
The showstopper of the game: there is no original music. All the music is excerpts from various ambient musicians' discographies (Loscil, Gas, Biosphere, to name three). Great advertising technique. I have since bought many of their albums, and I owe it to Osmos for introducing me to ambient music. Not only does it fit the game perfectly, it's good on its own as well.
Give Osmos a try. It's a unique game dynamic and I hope they do more with it in the future.