Add brush styles and opacity : it allows for highlight, pressure pen, neon, embossed, spiderweb...
It would be nice to get more brush styles. The pressure sensitive option would be one possible style. Highlighting would be another one. In FreeNote, there is also the spiderweb, the neon and the embossed brushes that are very interesting.
Michael Vogel commented
Would also be fine to summarize useful brush settings (size, color, type) to a pencil case, to allow a quick access to these brushes/pencils.
So I would define a blue ink and a thicker red pencil and it would be easy to switch between them.