Halo 4 and Call of Duty: Black Ops 2 shoot it out

About 350 developers worked on Halo 4 at Microsoft's studio 343 Industries

He's been missing - presumed dead - for more than four years, but it's time to reactivate sci-fi gaming's most famous super-soldier.

Master Chief is back from deep sleep for fresh firefights with old foe the Covenant - a military alliance of aliens - and to explore a jungle and other landscapes on a planet created by a mysterious - and very violent - race known as the Forerunners.

Halo 4 marks Microsoft's big bet for Christmas. But it is far from being the only first-person shooter (FPS) targeting gamers this season.

Activision's Call of Duty: Black Ops 2 will challenge it for dominance a week later. Partly set in 2025, it marks the first time the series has taken place in the future.

The scenario - involving China's refusal to sell rare earth minerals to the US - was dreamt up by a leading US think tank. The embargo results in battles involving hacked drone warplanes, robots and the potential for global armageddon.

Both titles also face a potentially more dangerous foe: Audience indifference.

Cyber-terrorists take control of US drone aircraft and turn them against the country in Black Ops 2

A recent study by consultants NPD indicated that the number of people playing console games in the US - the world's biggest market - has started to shrink.

Sales are also down, due in part to tablets and smartphones offering much cheaper titles.

To make matters worse, a third highly-anticipated FPS, Medal of Honour: Warfighter, recently launched to a barrage of negative reviews, prompting publisher Electronic Arts to cut its earnings forecast. The firm declined to comment further.

Several critics described the title as "derivative", prompting talk of a backlash against the genre. The games industry is well aware of the risks of a category going stale.

"Historically there have been moments where franchises have fallen out of style," says Piers Harding-Rolls, head of games research at IHS Screen Digest.

"The music game genre was a very boom-and-bust experience - that was very popular for two to three years and declined very rapidly when people got bored of the type of repetitive experiences that were coming out.

"First-person shooters are still one of the most popular genres in terms of games, but it's inevitable there will be some sort of fatigue from year to year as you get through the progression of the franchises."

The challenge for Halo and Black Ops is to prove they have something new to offer.

Character-driven

Kiki Wolfkill, Halo 4's startlingly-named executive producer, believes part of the solution is to transcend the genre's bullets-and-lasers roots.

Medal of Honour: Warfighter based its missions on real events, but failed to impress the critics

"For us, we were specifically shooting for a level of emotional investment in the characters and what you were doing," she tells the BBC.

"Master Chief is clearly a hero but, some would argue, he was a little too much of a two-dimensional hero.

"What we really wanted to explore was what it takes: What is the sacrifice that you have to make, what are the vulnerabilities and challenges and fallibilities that actually make up a real hero?"

Offering a pre-determined narrative carries risks. Although early reviews of Halo 4 have been positive, some have criticised the linear nature of parts of the gameplay.

The last Call of Duty title, Modern Warfare 3, faced a similar reproach that players had little real control beyond running, ducking, aiming and firing.

"I invented a word, I called it an un-game," says John Walker, editor of gaming site Rock, Paper, Shotgun.

"I use it to mean games that don't seem to actively want your participation. You're not allowed to decide what you're going to do, you're not allowed to choose I'm going to go over there and fight them from that point, because if you do the game will stop you, or have an invisible wall.

Master Chief comes into contact with the Forerunner aliens after being dragged to one of their planets

"You have to follow their script or the game will baulk at you."

Treyarch, Black Ops 2's developer, was aware of the criticism.

"Call of Duty has always presented a cinematic linear story for players," studio head Mark Lamia acknowledges.

"What we wanted to do was offer much more player choice than ever before.

"There's branching storylines that we're introducing, which means the choices players make will at times have a significant impact on the narrative.

"Players will have key members of their team that could be in life-or-death situations that they can make a choice on, based on what's going on in the world. And the outcome of the future Cold War is affected by the decisions that you make and the gameplay that you take on."

However, much of this choice remains limited to side-missions, so critics may remain on the attack.

Seasons and leagues

The introduction of leagues to Black Ops 2 is designed to match up players of similar skills in multiplayer games

Beyond their main single-player campaigns, both games hope to distinguish themselves by introducing new multiplayer features. These can be critical to convincing consumers to hold onto their discs, preventing them from being sold to the second-hand market where sales do not benefit the publishers.

Halo 4's new Spartan Ops mode is perhaps the most radical move. Up to four players can team up to complete a "season" of 10 interlinked episodes released one week after another. If the main game is movie-like, this is the equivalent of a spin-off TV series.

"I think there's definitely something interesting in looking at how people are looking for these smaller moments of entertainment," says Ms Wolfkill.

With over 25 million copies sold, the first Black Ops title is the bestselling ever console video game

"We're intrigued by the idea of programming, and this combination of storytelling and co-operative gameplay."

There is - as yet - no guarantee of a "season two", but the potential to make and sell add-on series has obvious appeal.

"It's definitely something we're thinking about in terms of how you keep people engaged over time instead of relying on these monolithic giant releases," Ms Wolfkill adds.

Black Ops 2 takes a different approach, focusing on e-sports, rather than additional storylines. Players are now arranged into seasonal leagues based on their aptitude.

"There are people who skill-wise have had a difficult time enjoying and competing in the [mulitplayer] game because they got hammered by the other players," says Mr Lamia.

"We will figure out your skill after a couple of matches and work out your division.

"We just feel like it's not a lot of fun if you're always getting pounded on, and it's not that fun if you're always winning by a lot."

Each episode of Halo's Spartan Ops features its own computer-animated cutscene

Users can also take turns providing match commentaries - called "codcasts" - and there are new features to help spectators follow the action.

Previous Halo and Call of Duty titles have generated billions of dollars in revenue and are as close to a sure-fire thing as the gaming industry has, thanks to their fanbases.

But to avoid diminishing returns, the franchises must still convince a wider audience the FPS genre can deliver fresh, innovative thrills.