It's hard to get a game much simpler than Particles. There's a playfield with a bunch of red balls bouncing around it, and you, the blue ball, have to avoid the red balls for as long as possible. As time goes on, more and more red balls get added, making your task more difficult.
The music is kind of nice (the opening reminds me of Greebles -- now there's a game I'd like to see remade) and the sound effects are crisp. The physics, while simple, is done correctly -- not all balls have the same velocity, so a nearby collision can suddenly propel an otherwise-innocuous ball toward you at high velocity, which can be quite startling.
Overall, this is well done for what it is, but it's a little too simple to remain interesting for long. Like many, many other games in this list, I played it long enough to get the badge and that was about it.