Originally Posted by
Kathranis
There's not a ton of concrete info, but from what has been revealed/leaked, the setting and aesthetic were Overwatch-esque, and it was an FPS. In fact, most of the OW launch roster originated from class and NPC concepts for Project Titan, as did some of the maps.
It was a futuristic setting following an alien invasion, with mythological places like Atlantis and El Dorado reappearing. The basic setup was actually broadly similar to that MMO The Secret World, with secret societies vying for control of these ancient sites and the relics within.
They mentioned at Blizzcon that Overwatch was the name of one of the factions in the game. IIRC they were going to have three player factions, seemingly with different appearances for each class depending on faction, since leaked concept art includes some "terrorist" variants. The Junkers were also an enemy faction, inspired by Mad Max.
Prototype classes included Ranger (Soldier 76), Jumper (Tracer), Reaper (Reaper), Juggernaut (Reinhardt), Engineer (Torbjorn), Assassin (Hanzo/Genji), and Archon (Mercy).
One of the core concepts was a super hero-style double life system. Players would moonlight as members of these secret societies, being dispatched on missions around the world, which is where PvE and PvP would take place. Then they would have their secret identity where they'd have a day job (professions), home (player housing), social features, etc.
They did lots of prototypes, but apparently it never came together in a way that was fun. Metzen himself said the team "got squirrely" and it seemed to lack a strong direction to hold everything together. Supposedly everyone was just kind of working on what they thought was cool, pushing their own ideas, and sometimes undermining other people's work to make sure their stuff took priority. Allegedly the PvP component was the only prototype that went anywhere.
After Project Titan was cancelled, the team was broken up, most of the staff got reassigned, and a skeleton crew was left to pitch a new project, dubbed Project Prometheus.
For Prometheus, like OP said, they spent six weeks developing three pitch decks, two weeks each.
First was a StarCraft MMO that had a "settlers traveling the frontiers of space" vibe, which birthed the character McCree, based on an old Terran Prospector illustration Metzen did for the original StarCraft.
Second was Crossworlds, the brainchild of Metzen. Sci-fi MMO set on a galactic hub world.
While pitching classes for Crossworld, the lead class designer Geoff Goodman told Jeff Kaplan he wished they could do a game with 50 classes, but instead of like 12 abilities they'd each have three or four. But that would be impossible because they'd need to create 50 armor sets and unique weapons, etc.
That inspired Kaplan to come up with the third pitch, a hero-based shooter where instead of having classes there were just a ton of predetermined characters with unique kits comprised of a weapon and a few abilities. He repurposed concept artwork from Titan to design a dozen or so characters, then asked the team to go home and brainstorm heroes of their own. The next day they brought in dozens of possible heroes. Everyone got super excited and decided this was the idea they should pitch.
They pitched it to the board, and Kotick was apparently so stricken by the "hero lineup" poster that he stood up and gave them the okay, but due to the cancellation of Titan, required that they produce a fun prototype within six months before they'd get a full greenlight.
And so Titan became Prometheus, then Overwatch. Even though concepts were reused from Titan, the game engine and assets were built from the ground up.