It's more like infamous, you fly around, kill baddies, save the world, etc.
plus zombies

It is so much better.

Except for the third person perspective the 2 games have nothing in common. :)

What would make you think they were anything alike? Prototype is the spiritual successor to Hulk: Ultimate Destruction, Darksiders is a great mash-up of Zelda, Devil May Cry, and in the case of Darksiders 2, Price of Persia.

Prototype is an alright game but nowhere near as good as Darksiders in my opinion. They're also different types of games.

is farmville like mass effect?

The story is not good imo, but it has some fun moments.. defently worth to buy the pack, its cheap as hell.