Bioshock could be called one of the first truly next-gen games of this current generation, something that couldn't be done before. Ken Levine, known for his work on System Shock 2, brings us a very-well written, atmospheric first-person experience, with game mechanics that had never been seen before up to this point, making it the most revolutionary FPS since Half-Life 2. It's the second greatest experience I've ever had playing an FPS (after Half-Life 2, of course). A game that's so good that there was no way they could ever create an ending that would have lived up to the masterpiece that makes up the majority of the game. Despite having two somewhat ho-hum endings (based on your karmic actions throughout), I sincerely doubt that there was any way this game could have been better.
The survivor of a plane crash in the Atlantic Ocean, the main character, Jack, swims to the nearest thing he can find, a lighthouse. This turns out to be the entrance to one of the most wholly atmospheric cities in all of gaming, Rapture, an underwater utopia gone wrong, destroyed by pseudo-drug abuse, and an ongoing feud between two high-level archenemies, Andrew Ryan, the founder of Rapture, and Frank Fontaine, the "reaper" of Rapture.
You come across a man who is in trouble, via radio, by the name of Atlas, who needs your help to rescue his wife and son, and escape this hellhole. A woman by the name of Tennenbaum needs your help in rescuing grimy little "girls", called Little Sisters, who carry the one thing every insane junkie in this town needs, ADAM. ADAM is the currency used to purchase EVE-related products, which include a variety of gene-spliced abilities known as Plasmids, which are basically a form of scientifically-explained magic. These girls are protected by (unprovoked) gentle giants known as Big Daddies. In order to save a Little Sister, you must dispatch the Big Daddy that escorts her. Of course, you don't have to save them, and can instead commit the unforgivable sin of harvesting one for the ADAM she holds. Doing this, however, will affect which one of the two endings that you'll receive.
Many more stories co-exist in this underwater, which you can learn about by picking up recordings littering the game space. The recordings fill in the tale, offering a much more satisfying narrative. If you're a sucker for story, be sure not to miss a single recording, some of which require more exploration to find than others.
Bioshock, as well as with the non-linear narrative, also differentiates itself from the vast majority of FPS' by ditching the usual two gun rule, by allowing you to "hoard" your weapons; as well as health packs, and EVE (which powers your various plasmid powers), lending itself to a non-traditional and long-term combat experience. You can pick up med-kits and EVE, as well as ammo and such, at various vendors spread throughout the city. You can also hack said vendors, to get a discount, via a fun little minigame that gets VERY progressively hard as the game goes on, and rightfully so. The ADAM you get from saving/harvesting Little Sisters can be used to buy plasmids and plasmid accessories at the Gather's Gardens-brand vending machines.
The main star of the game is the chilling atmosphere, which makes for an immersive experience that hasn't really been matched, or even challenged, to this day. The non-linear well-written story, the complex, likable (or loathsome) characters, the well-designed, spooky game space, and vastly varied splicer enemies that come at you with all sorts of different abilities force you to think on your toes, and make you utilize every weapon in your arsenal. There are plenty of details shoved into the many nooks and crannies, creating a very authentic feel to the environment. This all comes together to create an absolutely unforgettable narrative, whose only (post-beginning) cutscene is one of the finest and most utterly flawless scenes in all of gaming. Even if the last 10-20 minutes seem to slog a bit, and fail to live up to the quality of the rest of the game, I honestly doubt there is any ending they could have had that wouldn't have been a disappointment, a tell for a truly top-notch game.
Bioshock is a masterpiece of storytelling and atmosphere, and the gold standard for which all story-driven FPS' should aim for, a standard that has rarely been matched since.