After seeing Auditorium in a recent indie bundle, I realized that it had finally come to Steam. I had paid for this game a few years ago, and enjoyed it. Fortunately, the existing account I had at the developer's site had a way to generate a code to redeem on Steam, along with a stand alone download. Both worked magnificently.
Auditorium is a music puzzle game. All levels have a particle stream (sometimes a few!) which must be directed around the level towards containers. There are a limited set of elements that are used to manipulate the stream. They make the stream go in a certain direction, go faster, spiral in, repel, and block, among others. The intensity of the effect is determined by the size of the element. Interactions between them are common: spiral + go faster makes a curve in the stream, for example.
As the containers fill up, a lovely orchestra piece starts playing. Each container controls the piano, violin, bass, or some other part of a larger piece. These are just 10 to 20 second samples; they seem to be original works, so don't expect Beethoven's 9th here or anything. Every level only has a portion of the whole symphony. Levels are grouped into acts, and each act has it's own soundtrack.
To complicate matters, some containers require the stream to be a certain color passing through them to fill them up. This is usually provided by clearly denoted areas on the level, but sometimes the elements themselves change the color of the particles as they pass in and out of them.
What I enjoy most about Auditorium is the fact that I can't get frustrated at it. If I'm stuck, I start playing around, and enjoy the symphony fading in and out as I fiddle around with it.