First off, I had no idea what kind of game it is, never played System shock games for example(now I've played through the second one thanks to GOG and I warmly recommend it to everyone). So upon entering the game I encountered my first problem, there was no music! I managed to solve the problem but it was pretty damn annoying. I glad I didn't give up on it.
Going underwater was magnificent, atmospheric and beautiful. Never have I seen such a great water effect in a video game, flowing, reflecting etc.
Descending into the ruins of Rapture, uncovering the events that took place years ago,with audio tapes was the real deal.
Combat-wise it was pretty nice too. I played on the hardest difficulty, and I had begin to suspect that it's pretty dumbed down thanks to the console version, but than I met my first Big Daddy. Needless to say I died a miserable death, and recovered in the nearest vita chamber. Now I approched the situation with more finesse, taking a hacked security bot alongside to aid in the battle. I sweated blood but finally put him down for good. What a battle!
The "big" moral question the game brings up first is what to do with the little sisters? Of course I didn't have the heart to harvest her, and in my opinion this choice is not as grey as it should be. But you can easily forget about it when you finally meet the infamous Andrew Ryan. It's the climax of the game, hands down. The monologue is very thoght provoking, and have a great dramatic effect. After kindly obeying Andrew, appears the new villain, Fontaine. It kind of a setback, you are not as motivated to play the game as in the beginning, but the combat still carries the game on it's back.
Bioshock obviously have it's flaws, but the atmosphere it creates ,and the deep story it delivers easily make it one of the best game of all time.