Through PC Gamer, that is, revealing many a thing: from Episode Three being set in the arctic to gameplay with Alyx and the 'Hunters' of Episode Two and what have you. Here's a select slice from it:

As for Antlion country... you know how they burst up from the ground, having burrowed towards you via a network of underground tunnels? That's where you'll be going. These tunnels are rather pretty thanks to new flashlight shadows (think Doom 3) and a special shader-effect Valve have devised specifically for bio-luminescence (you have to love them for that). But in and around them, you'll be hounded by the hideous new Worker Antlions. When I tell you these spit poison, you'll probably imagine the half-hearted hocking of the Bullsquids in the original Half-Life. This is more like a Howitzer. Their venom is so corrosive and spat with such force that it actually smashes through almost anything between you and it. If it hits you - and it usually does - the liquid blinds you and the venom burns through your health. And in case that doesn't make them hard enough to fight, they hop around like hyperactive locusts.