Liferaft Zero casts you as a test subject negotiating a series of challenge chambers in a stark, sterile lab facility. You are encouraged to complete each task by an unsettlingly cheerful narrator whom you suspect might not be quite as they seem.
Yet it's not Portal, it's not played in first-person and you're not equipped with a portal gun. Instead it's closer to something like N+ where you can leap inhuman distances and wall-jump with aplomb. You also have a grappling hook and often find yourself swinging from hook to hook over pits of deadly spikes.
It's derivative, sure, but it's also well-designed, and not just from a gameplay and visual perspective. What really impressed me was the audio, particularly the way the sound effects of your exertions echo around each vast test chamber.
Liferaft Zero [Mikengreg]