Plague Inc was one of the best ever phone games, and it's still outstanding on the computer.
Varied and challenging scenarios each step of the way, in your mission to infect the world and kill all inhabitants. Every scenario requires you to rethink your strategy, and often opens up different symptom or infection options, which makes it fun to play. It's the right kind of challenging, but if you get bored just choose the mega brutal play mode next - you won't be disappointed.
The news ticker that's updating you on world events is everything from helpful to your mission, to hilariously clever.
Some combinations of symptoms create gems such as the Brown Streets: Public Defecation combo.
Compared to the phone game, this version of the game lets you play at triple speed, which takes some of the waiting out of it (not that there was much of it in the first place). Way to go once you've got the hang of it.
The game is a must have, with high replay value.

The only mildly negative thing to say about it is, that it plays better on a touch screen device. Popping a lot of bubbles at once is easier to do with two hands. This would only be an issue until you unlock the 'Metabolic Hyjack' modification though, which auto-pops the orange and red bubbles for you .