The age of the engine means it doesn’t work on me now, but on the first HL1 playthrough, my embarrassing vertigo kicked in when I was shuffling nervously along high-up cliff edges during one of the earlier outdoor escapades. So I faced the wall, walked sideways and refused to look down – a plan that rather fell apart when murderous soldiers started shooting at me. It all seemed so impossibly huge, like I’d been locked in a car boot for three days then suddenly awoke to find myself parachuting out of an aeroplane.