When Half-Life 2 ended it left so many questions unanswered that the sheer horror and frustration of fans that the rest of the story may remain untold for at least another half a decade, was almost palpable. Thankfully, due in no small part to the advent of content delivery over their Steam system, this heart-breaking wait is not to be.

Having grappled the content-delivery bull by the horns and proved that Steam is an effective tool for this, Valve have now moved on to the far more challenging main event: setting out to show that Episodic Content is not just the latest in a line of nasty buzz words.

Whereas the expansion packs for the original Half-Life dillydallied around the fate of Gordon Freeman and placed you in the role of bit players, this time the expansions are set to give the player exactly what they want - a direct continuation of what happens after the explosive events atop of City 17’s Combine Citadel. Promised in three chapters, first out from the pen is plainly titled Episode One. Only a maximum of five hours long, the game proves every step of the way that content is far superior to length.

Half-Life 2 was a gaming world stuffed full of ideas that left the player with a lot of ‘what if?’ questions. What if Combine soldiers were pitted against zombies and headcrabs? What would it be like to get up close and personal with a Stalker? While there have been countless fan-made mods that allow this, no one knows their own content better than Valve and perhaps more importantly, how to deliver it in a cohesive and exciting way. For this reason Episode One satisfyingly gives the player exactly what they’ve been itching for. Placing them back in the now-ruined streets of City 17, you as Freeman are given a chance to witness up close the destruction brought about by your activities in the Citadel – during the initial game the city went through stark changes from Orwellian Dystopia to urban combat zone. This time the change is even more startling and portrays a city literally on the verge of total annihilation. With their grip shaken, and the city devastated, the Combine are attempting to take back what little remains. The Resistance on the other hand are trying to ensure as many civilians as possible can escape.

Back for the roller coaster ride and playing a far more pivotal role this time around is Alyx Vance. Previously she and other characters like Barney Calhoun acted as supporting characters who popped up to accompany you for a little while, but here the game is almost exclusively played with her by your side. Rather than breaking the atmosphere that fans have come to relish, the player will be grateful for having her as company - not only as back up in numerous tight spots, but for companionship during the pitch dark of the underground sections. These areas play like the terrifying village of Ravenholm but with the tension meter ramped all the way up thanks to the confined spaces and Gordon’s dodgy flashlight. When the battery runs out and there’s no other source of light, the shuffling sounds of an approaching monster somewhere in the darkness is enough to have you hammering the flashlight key in sheer panic...

Thanks to the Source engine's new High Dynamic Range lighting, first shown off in the Lost Coast demo, the sights of City 17 are all the more impressive and put to bed much of the moaning about the game having lost its initial graphical appeal. In particular the moments where you step out from darkened corridors or underground areas into the hazy fading sunlight, are something to behold.

With Alyx playing such a pivotal role this time around it’s good to see that she’s been given an overhaul. Improved animation makes her expressions and actions feel more realistic, endearing, and more alive than ever. Shine the torch in her eyes and she’ll flinch. Let the flashlight cut out and get caught in total darkness and she’ll sometimes decides to try and freak you out by imitating a zombie before yelling “Gotcha!”. While a pretty stupid thing to do to a twitchy one-man killing machine who’s armed to the teeth in zero visibility, it is a good example of how Valve have tried to make her behaviour seem much more human. The fact that she doesn’t do this every time the light goes out is one of those little touches that can make or break and the sort of thing that is also applied to parts of the environment and settings (although to say much more would spoil some of the surprises).

That’s not to say everything is perfect and although an extremely rare occurrence Alyx can sometimes bump you off ledges to your death. It’s also worth mentioning that along with Gordon’s new friend comes another appearance from everyone’s favourite mechanoid, Dog. His screen time is again limited, but for the time he is around the player will be reminded of exactly why he was initially so impressive.

Short it may be, but that isn’t to say that Episode One feels lacking or just tossed together. Admittedly it would be hard to break the things that made Half-Life 2 so great, but it would have been simple for Valve to throw something out the door in a bid to cash in on the series. Instead they’ve done their usual superb job of polishing it to a gleaming shine and listening to the included developer commentary gives an indication of just how much time and effort went into putting it all together. While there are no new weapons or toys to play with, the emphasis is clearly on progressing the storyline, with the all-new stuff promised for later chapters. The game's pacing as the pendulum swings from action to intrigue and tension is a masterstroke with so many memorable sections in such a short space of time that the player will be left breathless and, just like the end of Half-Life 2, wanting more. The game may answer some questions but it certainly introduces a crate load of new ones that demand answering and unsurprisingly the ending is the usual sort of cliffhanger that fans have come to expect. Deep down they surely wouldn’t have it any other way.

With Episode One Valve have proved that episodic content can definitely work and once again raised the bar. Only Episode Two will reveal if they can continue to beat their personal best.