When I first played Prey, I had no idea what to expect, and as a result the game's introductory sequence made a profound impression on me. If you haven't heard much about the game, I recommend you download the demo or the full version and try it out before you read any further.
Prey is a survival horror first-person shooter adventure game that pits Tommy the Cherokee against an invading horde of aliens intent on harvesting their human crop. The protagonist's Native American heritage is relevant because it serves as the plot justification for a number of special abilities, such as resurrection after death and the ability to move out-of-body in a way that introduces puzzle platforming elements to certain parts of play.
While Prey is quite evidently influenced by sci-fi fare that preceded it - for example, the alien language of the Hunters sounds exactly like that of the Protoss from Starcraft - it has also had influence of its own. The developers ostensibly came up with the idea for incorporating portals into the gameplay way back in 1995, and whether or not that was a novel concept at the time, Prey did beat the popular video game Portal to the orange-and-blue momentum-preserving windows in space, albeit in an iteration more circular in shape. Prey was also remarkable for its time in the novel ways it deals with resurrection and alteration of gravity.
It certainly has its flaws. Heavy use of expletives dilutes the meaningfulness of diegetic dialogue and the game teeters on the edge of having too many game mechanics and concepts to provide a cohesive experience. (Expletives can be turned off, but I'd certainly not recommend this for younger players based on that feature alone.) Even so, I do recommend it for those who enjoy the occasional massacre of evil aliens.
Sam's Protip: Using the right-mouse button executes a variant attack with your selected weapon. A variant exists for each weapon in the game.