We all had different reasons to love this game, but what made it special for you? 
 
For me, it really went above and beyond what any other game has done in regards to really immersing you into the world of Rapture and making you feel like you were there. It almost made Rapture feel like a real place, which is just amazing to me. I felt like I was controlling a real person somewhere far, far away.

It wasn't special for me. It was just another good FPS game. I liked the character of Andrew Ryan and the game's lighting but I couldn't follow the plot at all (I was only half paying attention in the second half). I still don't have a clue why I had to fight Seth at the end.

" It wasn't special for me. It was just another good FPS game. I liked the character of Andrew Ryan and the game's lighting but I couldn't follow the plot at all (I was only half paying attention in the second half). I still don't have a clue why I had to fight Seth at the end. "

I did like the combat but the real special thing about Bioshock for me was the environments and the whole story and way it was told.

The setting. It was nice, and also really fun to play. Also, the story was catching, and I really wanted to find out what the hell was going on.

All the little girls.

BioShock was all about the setting for me, Irrational did an excellent job in creating a decayed underwater 1940's Utopian city. Plasmids were cool and all but Rapture was the real star of the game for me.

The atmosphare and the stroy. The story isn't all that good I think, but it's interesting enough to keep me going. Gameplay wasn't that good at all though. That is the main reason I havent played the sequal. The gameplay is simply boring in my opinion.

The chilling atmosphere. It made me want to explore  Rapture and figure out just what the hell happened. The art deco style mixed with era specific music really made you feel like you were in the 40s. The ghostlike occurrences and the discovery of left behind recorders were an excellent way of unraveling the story. The way the game ended felt very rewarding. Reason being is because it didn't end with some crazy cliffhanger like almost every game does today. I love the assassin's creed games but it drives me nuts everytime I finish one. Cliffhanger endings are great but when you know the story won't be finished for another 1-2 years, it can be frustrating.

Rapture.

The only thing that got me through the game were the story and atmosphere. I absolutely hated the combat, but because I wanted to explore Rapture and find out what went down I stuck with it. 

The atmosphere was the key factor for me. I genuinely wanted to find out what happened down there. The story and characters just held everything together, and made the trip to Rapture completely worth it.

Unique setting, immersive atmosphere, story was decent enough.  I still didn't finish it.

" Rapture. "

Bioshock remains one of the most immersive games I've ever played. The way the story is told through various radio diaries you find throughout the world means you only get as much story as you are able to uncover. Forgoing the use of cut-scenes to keep the story moving was one of the best choices that game made and I hope more games take notice and utilize a similar mechanic in the future.
 
They also did a great job of making one bad guy in particular a mini-boss every time, because taking down a Big Daddy is a process that you can't waltz right into and expect to be successful. The sequel took this idea to the next level, but the original provided some memorable moments courtesy of one of the best adversaries in gaming history.

I firmly believe the graphics are fantastic. The water in this game is probably some of the best water textures i have seen? 
 
Rapture came to life for me, and that's what i like in a great video game. The whole idea of it being under the ocean is mind blowing. It was actually one of the only games that i foun sort of creepy or disturbing in some aspects. The dark damp setting, the Splicers (especially those Paper-mache splicers :S) it was all great.
 
The music also made it feel like you were in the specific time-frame.

" The setting. It was nice, and also really fun to play. Also, the story was catching, and I really wanted to find out what the hell was going on. "

" Cliffhanger endings are great but when you know the story won't be finished for another 1-2 years, it can be frustrating. "

That a man chooses, and a slave obeys.

I just watched it so I didn't get the full experience, but the environment design, and the discussions about ideologies beyond the old narrative standbys was refreshing.

" I firmly believe the graphics are fantastic. The water in this game is probably some of the best water textures i have seen?"

It's special cos it's just so fucking different. All the other games  weren't even allowed to have children in em, like GTA 4, Fallout or Mass Effect. In Bioshock you literally hunt kids and rip them open. For genuinely interesting reasons.
The enemies are just fabulous. When you're not attackin em, they're still doing things. Like that splicer guy who'd walk around singin "Jesus loves me this I know, For the bible tells me so" or you'd catch one tryina steal things out of a vending machine, the big daddies completely ignore you. Actually most of the enemies are a bad sad in one way or another, just cos their life is so fucked.
Then there's the end where the game wins you.
Everything about it was just fuckin bananas.
Also using powers on guys is fun and I like setting crazy huge traps.
 
Here's a creepy old video that says a lot about the original Bioshock:
 

" @atomic_dumpling: What?! Are you serious? That's crazy man! Never knew that at all. Well, looks like it was successful for them, because the water is fantastic. "