I have found that rhythm defines the feel, perceived genre and atmosphere of a piece quite as much, or even more, than the type of harmony and melody used.
Composite meters make the polka and waltz into what they are... And then there are techno beats, goa beats, african beats, cuban beats, jazzy beats and rock beats...
I was looking around for resources on this subject for quite a long time, but the best source I have found so far was to listen to music.
If anyone knows of online (or offline) sources of rhythmic coolness - for example currently I'm really interested in how rhythm is used in folk music around the world, it seems like an infinite treasure trove -, or ideas to share on this subject, it would be really cool.