Great Idea, But Difficult to Execute Properly
First off, let me just tell you how great of an idea this game was, and that I thoroughly enjoyed it. I played through a total of 3 times, each time learning more about what I needed to do, finally decimating all countries except Madagascar and Greenland. However, there were some problems.
It seems like it would be impossible to fully please any of the people writing reviews (including myself) with a game like this, because it seems really tricky to fix everyone's complaints while still keeping a good game.
My one big complaint that I'll talk about is visibility and lethality. I found out that the best way to spread the virus is to keep 0 visibility while making it highly infectious. I did this by only keeping a fever, then investing all my points in making it easier to transfer and more resilient. However, even though my visibility and lethality was basically 0, people started to die and countries closed their airports and borders and such. That didn't make much sense to me. Of course, keeping in mind that this is a game, you can't just make it so easy that by making a similar virus you can infect the whole world, then turn the lethality up. It would be boring and formulaic.
The only thing I would suggest to fix this is to have more items contribute to the visibility and lethality meters. For example, if a virus has infected a water supply and half of a country's population, it's obviously quite visible. Also, if a virus is highly resistant to drugs, it should be far more lethal. Currently, these items don't contribute to those meters, and it confuses the player when borders start getting shut down and millions of people die from a simple fever.
Overall though, stupendous job, and I hope to see a Pandemic III.