It is therefore important to view Episode One as five levels from a larger fifteen-level game, because expecting the same variety and pace as a full game from a shorter Episode will lead to disappointment. Within the context of the Episode, puzzles and gameplay sections can feel overly long and repetitive. Within the context of the three announced Episodes that make up the post-HL2 story arc, we suspect they're about right.
Expectations duly managed, there is some cracking gameplay to be had. For starters, Alyx accompanies you for around 75 per cent of the game, a feature that Valve (the developer) calls 'single-player co-op'. She is a genuinely useful ally and, more to the point, genuinely well characterised. Valve claims to have spent a lot of time improving its facial animation and this has clearly paid off. Alyx is a fully-formed character who displays anger, fear, amusement, resigned lethargy and more when called upon by the storyline. Acting as narrator in parts, you really get a feeling that you begin to 'know' her - character creation worthy of film or TV.
There are stand-out moments in the game that she is crucially involved in. One section has you making your way through the streets of City 17, on the ground, while she covers you with a sniper rifle from several stories up. It works fantastically well, and is a good change of pace. Another part has her paralysed in terror in the dark, desperate for you to fend off an enemy that has surprised her. Yet another has her holding her own against wave after wave of zombies, as the pair of you desperately fight to hold out until a typically-unreliable elevator can whisk you both away from danger.
And it's these moments that really make the game worth playing. The set-pieces, the storyline progression - that's what makes Episode One worth sticking with. Make sure you keep that thought in your head, because there will certainly be points that make you want to cringe. Spending the first hour of the game with nothing more than the Gravity Gun doesn't exactly get you into the swing of things, and is right royally frustrating. Spending another hour or so almost in complete and utter darkness is not only dooming for those who value their eyesight, it also feels artificial. Other sections feel uninspired and on rails, with the linear path ahead of you laid out in an 'Energy Core Shutdown for Dummies' kind of way. While there were sections like this in Half-Life 2, they were quickly replaced by more interesting gameplay. In Episode One, they stand out because they are proportionally larger - at least until Episode Two arrives.