Pretty complicated and interesting strategy game to be honest, sure it only involves deadly diseases and viruses, but it has very interesting gameplay and brilliant tactics. As always your mission in Pandemic 2 is to spread the diseases and decrease human population dramatically. As you can see in this game you have role of evil mastermind.
From the beginning of the game you can select two different modes: realistic mode (main features of this mode include: all trait are available, longer gameplay than casual one and more in depth strategy than casual) and relaxed mode (this mode is different from previous one, main difference include: not all traits are available here, short and fast matches, less realistic and easier to handle). To be more specific and simple: first mode is hard mode and second mode is easy mode. Start playing from relaxed mode, get used to the game and after that you can fully enjoy realistic game mode.
After selecting your game mode you can choose which type of disease you would like to play with. There are three classes in total: virus (fastest evolution, most affected by environment, bonus to infectivity), bacteria (medium evolution, normally affected by environment, bonus to drug resistance) and last one is parasite (slowest evolution, least effected by environment, low visibility). Read description for each of the class and choose your favorite one. After that you can even name your disease.
Game offers tutorial, if this is your first time playing this game you should definitely watch it.
After tutorial you can enjoy game itself. You can collect evolution points and spend them on increasing deadliness of your virus. You can increase versatility and resistance to different drugs, you can improve symptoms of your virus, you can improve transmission and many other aspects which can help you to reach your goal in decreasing human population.
Game is pretty complicated and totally belongs to the strategy category, you will have to show your creativity and brilliant mind if you want to succeed in the game.