Unity is a gaming engine used for developing 2D and 3D games. Some of the major games developed using unity are temple run, robocraft, world series poker etc. Its main advantage is its massive cross platform support ( BlackBerry 10, Windows Phone 8, Windows, OS X, Android, iOS, Apple TV, Unity Web Player (including Facebook), PlayStation 3, PlayStation 4, PlayStation Vita, Xbox 360, Xbox One, Wii U, Nintendo 3DS line )and an easy-access user interface.
The official unity website has various tutorials and a complete online manual for nerds.
But before creating your game ,you must learn some game development basics such as game objects, scenes etc.
If you wish to learn it from scratch Walkerbrothers is an excellent tutorial website with great game walkthroughs. They also have an assessment at the end of each exercise(YAY! TESTS).
I decided to test it out by developing a basic tower defense game.
I have to say that it took me a lot of effort to finish this .I almost cried at the end , but it was worth it.
Unity also has an asset store for downloading various game objects. It even has a mascot called unity-chan. This asset store has many freebies which you can download and use in your game thus reducing our work.
My game has a platform made of around 600 cubes with crude little pink monsters made from a cube and a couple of cylinders.
My tower (the giant cube/piece of cheeze) has five lives which gets reduced when a monster attacks. The little blue diamonds are bombs which can be placed on the platforms by simply clicking. When monster goes near a bomb, it gets destroyed.
For doing it on your own go to www.noobtuts.com