The big surprise Blizzard had in store for Blizzcon 2014 was Overwatch, the first original IP from the company in several years. Overwatch is an online team-based first-person shooter, with a concept and style not dissimilar to Valve's Team Fortress 2. Like all other Blizzard games, Overwatch will be based on "Heroes", characters with unique abilities.
There is still no release date for Overwatch, but the game is already in playable form and there will be a beta in 2015. If you are interested in participating, you can visit the site playoverwatch.com, which apparently is not yet online. Overwatch was only announced for PC, although it seems to be the kind of game that can be easily adapted to consoles later.
More details coming soon.