I'll make the easiest criticism and just say that if you're building something with a stated goal of being "syntactic sugar", their hello world example is god awful...

From the README:

    .html {
        .head {
            .title {
                text: A simple Hello World example;
            };
        };
        .body {
            .div {
                text: Hello world;
            };
        };
    };

Just off the top of my head, compare that with Haml and let me know which one you'd rather type:

    %html
      %head
        %title
          A simple Hello World example
      %body
        #somedivid
          Hello world

...and that's assuming you couldn't replace Haml's %s with .s to match Nazca