One of the finest FPS worlds ever made.
There's hardly anything I could say (or need to say) about Bioshock that hasn't already been said countless times. This is one of the definitive games in the first-person genre, right alongside the original Half-Life and Deus Ex, for players who want a fully realized world to explore and riveting storyline to become engrossed with.
It's so rare for a game to hit a home run across so many facets, but Ken Lavine and the team behind Bioshock managed to pull it off. Never has a game world been tied together with such a distinct and well-executed art style, game and level design, sound effects, music and narrative. The underwater city of Rapture is fully believable. Its history, its architecture, its citizens and stories ... the overall effect of exploring this world is unrivaled in gaming.
Minor complaints are the lack of multiplayer, lack of replayability because you can master both guns and plasmids through one playthrough, and the overall narrative doesn't change much (if at all) regardless of the in-game choices you make.