If you are not familiar with Pandemic 2, then there is something wrong with you. However, this article is not about Pandemic 2, but about future game Pandemic 3.
If you could decide, what would you improve with Pandemic, what would you do? Of course more symptoms is needed, but I would also like to give more alternatives for spreading and hiding the disease. I mean, that player would have chances to put the virus in a ship and plan a route for it.
You should also have changes to influence on incubation period.