Particle Blow isn't really a game, just a little software-toy for prototyping a game mechanic.
A bunch (a few thousand actually) of particles start flying across the screen, and you can lay down arrow to affect their path. Click to place arrows. When you mouse over an arrow three little handles will show up. The "X" deletes that arrow, draging on the arrow itself will move it around the screen, and click on the handles at either end of the arrow allows you to adjust the size and direction the arrow points. Larger arrows shove particles around harder.

This game was completed in just a week. After a long time spent thinking how cool it would be to start doing a game every week like the Experimental Gameplay Project guys (here and here) and also more recently the Kloonigames guy and Prototyprally dude, I decided I was going to give it a shot for myself.

I don't think I ended up with something terribly fun, but it took only 1 week (I knew before I even finished, really) to figure that out. It does make an interesting thing to play with for a few minutes.