This what I call a truly flawless game. You've got everything in this game: you've got upgrades, you've got crazed enemies and you've got a real plot. The story is centred on you, a lost man who discovers an underground city called Rapture, a utopia city, a place developed as the result of some experiment gone wrong. In order to buy upgrades you must harvest ADAM from little sisters after having vanquished Big Daddies (sort of boss fights).
The gameplay is sort of classic: a FPS with deadly weapons. You've got the RPG system installed all over the game through the upgrades and the "magic" ( you can burn, freeze, use wasp swarms and other interesting powers to bring down enemies).
You can hack different things like cameras, safes or turrets.