The current design provides a very poor overview of things (especially discussion categories menu). There are lots of redundant vertical empty spaces and unnecessary text (especially description) that decrease the overall visibility and readability. It is not optimised for regular users.
My main suggestion is to at least reduce the vertical empty spaces between the text in individual boxes of different boards/categories (i.e. vertical space between “name of the board”, “description” and “number of posts”). In fact, the “description” can easily be removed from the boxes, while “last post” and “number of topics” can be put in the same line as the “name of the board”. The details can be put inside each board (description is already in the individual board on top).
The vertical empty spaces between the text can also be reduced in thread boxes inside each board.