BioShock look more UE3 than UE2.5. And now they're promising the same treatment leap for the UE3-powered (and still-way-off) BioShock Infinite.
"Right from the outset we realized that this was going to be a monumental undertaking on the tech side," Irrational tech director Chris Kline wrote on the dev's forums, "but decided it was a challenge that we simply had to take on in order to give gamers the kind of quality experience they've come to expect from Irrational Games and BioShock." Kline reveals that the team considered using the heavily modified Unreal Engine 2.5 they'd already invested in, but it was "too under-powered and unwieldy for the depth and complexity of the gameplay and narrative we had planned." So Irrational stepped up to Unreal Engine 3 and began modifying its base.