(CNN) -- While many people still associate Facebook games with casual offerings like Zynga's "FarmVille," the social media giant has expanded its game catalog through titles like KIXEYE's "War Commander" and Kabam's "The Hobbit: Kingdoms of Middle Earth."
Now, Facebook has partnered with start-up U4iA Games (pronounced "euphoria") to launch its first "core" video game, the first-person shooter "Offensive Combat."
The game, which had a soft launch three weeks ago, has already attracted over a half-million players with no marketing. The game is playable as a Facebook App and included in the Action games section of the site's App Center.
"Facebook wants to bring the next-level gaming consumer to their platform," said Dusty Welch, co-founder and CEO of U4iA Games. "Core games monetize the highest and are the stickiest."
Welch and co-founder and CCO Chris Archer have backgrounds that include having overseen huge franchises when they were at Activision like "Call of Duty," "Spider-Man" and "Guitar Hero."
Archer said his studio designed "Offensive Combat" for a fast-growing segment of core gamers who want a fine-tuned, shooter game that can be played anywhere, anytime via their Web browser, and not limited by the need for a major software install or dedicated hardware.
"Offensive Combat" is a shooter that blends elements from the most popular shooters out there like Microsoft's "Halo 4" and Activision's "Call of Duty: Black Ops II" into a free-to-play experience that's fully customizable.
Players can choose from 30 game archetypes like modern soldiers, space marines and robots and engage in a variety of multiplayer modes across nine maps. The online game will expand with new content every two weeks.
Players can purchase in-game items, including weapons, to further customize the experience. These micro-transactions will allow players to move through the progressive "grind" of leveling up and unlocking content, but Welch said the battlefield will remain even for all players.
"There are millions of consumers around the world who play core games and want to play these types of free-to-play games," said Welch. "First-person shooters have dominated gaming since the early days of 'Doom,' 'Wolfenstein' and 'Quake.' When you look at the success of free-to-play games like Riot Games' 'League of Legends' and Wargaming's 'World of Tanks,' there's room for a first-person shooter like 'Offensive Combat.'"
More than 251 million of Facebook's 1 billion-plus members currently play games every month. Even with droves of players leaving Zynga's games, there remain new audiences that haven't yet gravitated to the platform.
"Gaming on Facebook is all about connecting with friends," said Welch. "FPS games are the most social of all the core gaming genres. FPS fans want to connect with their friends and clans and do it quickly. What better, simpler way to do that than Facebook where there are a billion gamers? The problem has been that the genre hasn't been represented yet."
Michael Pachter, a video game analyst at Wedbush Securities, said the free-to-play business model is popular because it reaches the broadest audience, it's approachable and easy, and there's no barrier to entry.
"You can make $100 million off a game that's free to play like Riot Games' 'League of Legends,' said Pachter. "Free-to-play takes away some of the risk."
As much money as Activision and Microsoft have generated from billion-dollar shooters like 'Call of Duty,' 'Halo' and 'Gears of War,' Welch believes there's a much larger audience willing to jump into the genre without the requirement of a $60 disc. He also believes there's something to be learned from Zynga's failure to keep its gamers happy.
"It's crucial to continually innovate and stay connected with your community," said Welch. "The lather-rinse-and-repeat methodology that Zynga used too many times gets stale fast with your user base and they degrade and move on. We saw that happen in the console space with games like 'Guitar Hero' and 'Wii Fit.' True innovation creates a sticky audience. Zynga games didn't attract mid-core to core gamers and they flooded back out to 'American Idol' or whatever other entertainment is popular today."
Facebook has partnered with U4iA Games to develop new social mechanics that are being designed to build engaging gaming communities. These features will eventually debut with "Offensive Combat" before moving on to other Facebook games.
In the wake of the Sandy Hook tragedy, violent video games have come under fire in some quarters. Welch believes "Offensive Combat," which was designed as a mash-up of different constructs, offers a more irreverent and light-hearted approach to the genre than more realistic shooters.
"I'm a parent with two children and I believe it's the responsibility of parents to monitor and decide what's appropriate for their situation and we take that very seriously," said Welch. "Facebook is for people 13+ so there's age gating for that platform. While the gameplay experience was designed for hardcore gamers, you can run around in a banana suit with futuristic plasma weapons."