At first I confused your project with GtkD. I'll take a look at it, to see how it compares. Many examples for Gtk use C code, and I end up looking for the correct GtkD class that offers the function. Otherwise I quite like the classical inheritance that is possible with GtkD, whereas you use the "alias this" trick, which is fair enough. Also you can bind events like onExpose naturally to class methods in GtkD. There is no data pointer involved. On the other hand small executables are my cup of tea. I've compiled a small Haskell Gtk application, that weighted ~10 MB (stripped) and the same program in D using GtkD was 3.4 MB in size. Let's see...
-- Marco