A couple of random quotes out of a recent article in magazine PC Format (stolen from 3DR Forums, bwaha),
"Prey is based in a Dyson sphere, a monstrous construct with a small sun stabilised in the centre of a massive globe. 'It featured in an episode of Star Trek,' says Gerritson, though Rhineheart is quick to point out: 'We didn't get it from there; it was in Scott Miller's original design back in 1997, as it hadn't been done in a game before. The ship is also growing, expanding its flesh; it's not a complete sphere, you can see space and the Earth through it.' Broussard chips in, 'You'll gradually realise the ship is the primary enemy of the entire game'."
"Other Portals are one-way, or only temporary, with secrets hidden inside, if you're quick enough, and when you see a 'sphincdoor' for the first time you're going to be mildly disturbed - let alone the portals modelled after parts of the female anatomy. This game is going to be 18-rated, doubtless [This is a UK magazine]."
"3D Realms hopes that the plot and the innovative elements will be counterbalanced by more standard elements. 'We're going to give them one new element at a time,' explains Gerritson, 'ramp up the complexity of each slowly. Everything's going to be balanced; we record all of our play sessions to work out where the bottlenecks are; we collate all the data and graph that stuff, so we know where the player died, what their health was throughout, and what the stress points of each level are'."