Plague Inc: Evolved [Steam store page]
This game recently came out of Early Access after two years in development, but in my opinion it's still sort of a novelty item. The core gameplay is just a direct rip of the flash game Pandemic 2, with prettier graphics, along with most of the flaws of the original game.

Basically you're trying to infect and kill the entire world with your disease - but if it starts gaining too much attention countries will start locking down their borders, ports, and airports. If an island country does this in the base game there's no chance you'll win, since you have no way to spread there aside from air and sea travel. This doesn't really encourage much experimentation or fast gameplay, since getting discovered too early basically loses the game for you.

Some of the other disease types offer solutions to this, but they aren't really offered to the player in a logical order that would keep you interested. Each disease is unlocked by beating the previous, and most of the first set use the exact same tech tree with minor variations that don't impact actual gameplay aside from slowing down the speed. Fungal was especially brutally slow.

This definitely does not improve an already slow game about waiting for disease to spread, and popping occasional bubbles for extra points. I guess these bubbles are supposed to keep you interested, but I would have preferred just to be able to fast forward without having to micromanage them.

Several of the diseases with more interactive and strategic mechanics were pretty fun for a playthrough or two - for example the parasite let you hijack planes and fly them directly at a target country to infect it - solving the island problem I mentioned earlier.

There are also some fun variations with different themes - like a Santa version where you're spreading holiday cheer, and infectious vectors are things like Christmas Presents. I just wish the overall game wasn't so unlockable based so you could play the interesting diseases and modifiers, without dealing with the boring, bad, or exceptionally slow ones.

There's also a game mode where you have to actually fight a global CDC-type AI, making certain countries where they set up strongholds much harder to infect, etc. This adds more of a gameplay feel, although since your direct abilities - even things like zombie hordes - aren't very effective it can still be a bit frustrating. All the interesting abilities eat up your upgrade points, and these don't come in at a very satisfying pace in any game type.

Usually the upgrade points come in slow at the start, then you get flooded as the infection explodes and grabs all the new countries, tapering off again once most people are infected. A typical RTS-type resource model where the rate grows over time would probably be a lot more satisfying - tapering off into a useless drip feed of points isn't much fun.

There's also a multiplayer versus mode where you can battle a friend on the same map, messing with their disease and upgrade trees in addition to doing your own as normal. Whoever survives the longest is the winner, rather than having to take over the entire world.

So if you can grab it cheap on a sale it might be worth a look - but I doubt it will keep most people engaged for a significant amount of time. Sad to see for a game that's been under development for so long - really needs to be rearranged and polished to be a smooth and fun experience for new players.

Synopsis:Heavily based off the 'Pandemic 2' flash game, with added unlockables that really ruin the flow and make it feel like more of a toy than a polished game