
Second time through, I had all the time in the world to learn the nuances of combat, strategy with plasmids, and time to just explore the environment. This is the way the game should be played. It was stupid of me to form an opinion from just a 3-day rental.
The game truly is a very atmospheric experience. I actually took my time to notice little details in the game, and took my time learning the history of Rapture. The story is just...amazing, though it's essentially optional. You can get the gist of it by just a quick play-through, but to really understand the characters, their goals, their fates, you have to actively pursue that: collect all the audio diaries, listen to all the radio transmissions, and just observe the environment.
It's pretty amazing how the developers put a lot of thought into how the environment was set up. They didn't just throw some objects in a room randomly. They pretty much planned out each room to tell a story. Like you'll walk towards a room, and you'll have a ghostly vision of what had taken place in that room. Then what's left is the aftermath.

The same sorta stuff occurs in Metroid Prime, but instead of audio diaries they're text logs and the graphical detail isn't really there to present a story as strong as BioShock can. But still, I love this stuff.
So I take it back. BioShock isn't a so-so game. It's AMAZING. Go play it.