Spiral Knights Download is a game that allows you to test and develop the strategic vision of gamers. It is a free game very similar to the Diablo game as shown in the image below.
The game scenarios are all in 3D and the graphics are pretty good to be free. Also the creators of this game have put much emphasis to the special effects . You can access a wiki in which you can learn everything about the game. There is also a forum for generating discussions among players around the world. To play online you need to download the game first.