Bioshock

I rented this game a while ago, beat it on easy, and loved it, then I spied it on the shelf at the store for $30 and I had to have it.
I Still love it, the Story is Epic, the Plasmids make it possible to play any way you want and the characters made me laugh and (almost)cry all the way through.

Bioshock stars a Character named Jack(no last name is apparent, though a certain person in the game later appears to be your dad).
Who is in a plane crash in the middle of the ocean, he swims to a lighthouse that is near the site and enters the bathysphere he finds there, here you enter Rapture, an underwater city created by Andrew Ryan, a business man exasperated with the world's need to take his property for the common good.

Rapture is in ruins, the citizens have all gone insane after modifying their genes with Plasmids(genetic solutions that grant superhuman abilities).
The few people left sane are Atlas(a former smuggler and rebel, now just trying to escape), Tenenbaum( a scientist responsible for creating the plasmids, now repentant)
And Mr. Ryan himself.

Plasmids are made with a substance called Adam, which is made by little girls with Syringes called Little Sisters, who are protected by Hulking diving suit clad behemoths called Big Daddies.

As you advance you must collect Adam and splice yourself to gain abilities with which to fight, to this end you must kill the Big Daddies to get to their Little Sisters.
At this point one can either kill the Girls for maximum Adam, or save them and get less, though as a tip, killing them doesn't get an achievement, doesn't unlock certain REALLY cool powers and in the end gets less total Adam, Not to mention, you just feel good when the little girls thank you for saving them.

The story is well written, on par with Mass Effect, and ties more than enough loose ends up.
My biggest beef with it was Language and certain really sick things, like a mind control test playing audio of a strangling puppy, but they fit the setting, despite this issue I recommend this game to everyone.