Catman follows the life of a very interesting cat who get's himself into trouble often and hangs out with his enemies. (birds, mice, etc)
There really isn't a main plot, each episode is it's own little short story and most of them are quite funny, even though they have no voice acting, just music and text of what the characters are supposed to be saying.... Most of it's curse words....
Catman has a unique look comprised of the use of real photographs for much of the background and vectored art for anything moving, it's eye catching looks great though it may not be in everyone's taste.
The music is just frickin amazing, I think the music in this anime definitely goes up into my favorites of all time. I'm not sure what you'd call it but I suppose some of it might fall into the category of Jazz. It fits very well in with the events taking place throughout each episode.
The man of cats himself....is an idiot, in the best way possible. Let's just say anyone that can shoot down THE SUN is pretty awesome, or just pretty insane.
Overall I really enjoyed this series, it's just a short, interesting ride. I think it's worth anyone's time. (especially considering you can finish it in like under 30 minutes) Sorry I'm not more descriptive but it's such a short series that it's better to just watch it yourself.