The game is a team-based shooter that pits squads of six players against each other for control of various maps.
The characters that players control all have different superpowers that let them fulfil different roles, such as medic or tank, in their team.
Test versions will be released in 2015 but Blizzard has not said how much it will cost.



Abandoned project


Overwatch marks a departure for Blizzard which is best known for World of Warcraft - the long-running massively multiplayer online game - and combat game Diablo which are both set in fantasy worlds.
By contrast, Overwatch is set in the near future and revolves around small teams of super-soldiers that have individual abilities, such as teleporting, and equipment, including rocket hammers, they use to battle rival teams.
The skill in playing the game will come from combining different characters in the right way to unlock more powerful abilities, it said.
The success of the game is important to Blizzard because the numbers of people playing World of Warcraft is on a steady decline. Currently WoW has about 6.8 million subscribers, far fewer than the 12 million it enjoyed at its peak of popularity.
Blizzard showed off Overwatch and its initial roster of 12 characters at its annual Blizzcon gaming convention. More characters, locations and history of the world will be unveiled as development of the title continues.
Writting on the rock, paper, shotgun game news site Ben Barrett said the game looked to have a lot in common with the fast-moving Team Fortress 2 game made by Valve but which has Blizzard's "spin and polish on it".
He said it was "not the most original of ideas" and added: "Showing in what way they're different will be vital of course, to stop general cynicism getting in the way of people checking it out."
Mr Barrett wondered if the game has drawn on some of the work Blizzard did on a cancelled project called Titan. This was supposed to be a multi-player game set in the near future but Blizzard abandoned it after years of work.
Initially, Overwatch will just be developed to run on PCs but Blizzard did not rule out a console version.
People can sign up now to be part of the testing, or beta, programme for Overwatch.