EDIT: I just saw that you have already implemented something similar with a right-click and slide. Sorry, I missed this message on my first search through. So disregard this! Thanks for the useful software.
It would be great if you could change Q (and possibly also filter type) without having to go into the context menu. Some other EQ software I have used allows you to change Q by holding CTRL and rolling the mouse wheel. This gives immediate visual feedback on changes instead of having to guess a number and then see what effect it has in the graph. Perhaps filter type could be changed with some other combination of keys too (e.g. CTRL + SHIFT + mouse wheel to scroll through filter types).