It doesn’t stop there. When a Little Sister has harvested two lots of Adam it’s time to lead her to the nearest vent, at which point you can set her free or do some harvesting yourself. Whichever route you choose, you’ll incur the wrath of a Big Sister. A banshee wail screams out, the big music kicks in, and it’s up to you to scramble and find some way of stacking the odds in your favour before the gangly, suited harpy appears.
Fast-moving, brutal and heavily armed and armoured, the Big Sisters are all but unstoppable, and while you can, to some extent, rely on Vita Chambers and take them down bit by bit, you’ll have a much easier time of it if you plan ahead and use the same kind of tricks you use when defending against the splicers. Big Sisters can be stopped; you just need to use your brains to do so.
All of this is great, but it has to be said that, for the first few hours, BioShock 2 just doesn’t seem to have the magic of its predecessor. It’s hard to say why; the combat is better, the harvest/defend routine adds more variety, and the things that made the first game so atmospheric – the recorded diary entries, the excellent dialogue, the superb music, sound design and art direction – all work just as effectively as they did before.
Maybe it’s simply that you can’t help feeling that you’re playing a slightly less inspired version of BioShock, with the characters and plotline that made the first game so incredibly compelling replaced by new, lightweight substitutes. Even second-rate BioShock is great, and the range of weapons and plasmids gives it a flexibility and space to experiment that you won’t find in, say, Modern Warfare 2, but this just isn’t as spell-binding an experience.
With time, however, BioShock 2 blossoms into something different. It’s not just that the Little Sister stuff opens out the otherwise linear level design, or that the levels themselves improve (which they do). It's that the game suddenly finds its heart and establishes relationships and motivations that give you the will to push on through until the end. In these later stages the twist and turns of the plot are genuinely shocking, surprising and affecting, and I can’t remember a game since Ico where I’ve so much wanted to finish a game in one huge, breathless chunk. If the first two thirds of BioShock 2 are solid with sporadically awesome moments, the last third is pretty much magnificent. And this time, there’s a real sense that the choices you made - the moments where you took pity or revenge - mattered the whole way through. I won’t say more, you’ll have to play it.