Blast some Big Daddies!
Its hard to liken this game to any other, but I'd have to say its most like Fallout. Ammo needs to be conserved for the big guns, the Big Daddies. I choose to set free all the little sisters, and the game wasn't unnecessarily difficult at any point. There are lots of apartments and room to explore, turrets to hack, and upgrades to buy.
Top notch direction went into the game's style, and the game play is not far behind. This isn't a must play, but probably a should play, especially if you haven't experienced the freakish world of Rapture.