From personal experience, it's a pretty good run-and-gun shooter, with a well written plot.
However, I must laugh at anyone who says it's "the thinking man's shooter". Yeah, fine, the gravity gun can do some cool stuff, but really, most of the game is just run and shoot, use reflexes, and blow up any nearby exploding barrels.
Now, BIOSHOCK is a thinking man's shooter, since they give you so many options to deal with any number of enemy encounters, many of them smart (make big daddies fight each other, etc)