I loved the Ambiance theme developed by the Ubuntu folks.
However, it was too rounded for my taste. This theme is simply less rounded, has slightly modified window borders and uses a different button layout. Nothing else has been changed from the original theme.
I would like to add that I have no idea about building GTK and Metacity themes, hence my changes may not be entirely correct.
This theme works for me and I hope it does for you too.
If this violates any copyrights, please let me know.
Updated to use the new Ambiance theme available with Ubuntu 10.10
Include breadcrumbs in theme