when you open a mega menu that has subitems the subitems for the first category are already shown (on desktop, not mobile). That is to say the first category is already selected. Is there a way to deactivate this behaviour? In my customer tests I found that many people focus on the subcategories of the first (opened) category without noticing that there are more main categories to chose from.
One more thing form the customer tests: The image thumbs in the mega menu should definitely be clickable. I found your CSS solution in this forum (thanks!) but changed it in the code of the template < tb < menu < category.tpl line 75 which also works fine. So this is not a problem but I do actually think this should be the default behaviour.