No encounter ever plays out the same way twice. No two gamers will ever play BioShock the same way.
This is because the game has quite rapid respawn rate (enough rapid to be irritating and making the game into forced slugfest), causing encounters to happen even if not wanted and the creatures wander around aimlessly through the levels with apparently nothing to do. They sometimes huddle over corpses as if there was something interesting there, but there really isn't (I had scavenged all valuables from those corpses long ago).
Though I have to admit that I did play it on the hardest difficulty, so maybe that's (the rapid respawn) the only way they could think of how to make it more difficult. Didn't have much chance for stealth or alternative approaches when the guys were running everywhere.
Although it was advertized that munitions were supposedly scarce, I never really ran out of them, actually I was almost constantly maxed, except in the particular weapon I had taken a liking of and after fighting swarms and swarms of suddenly script-spawning enemies or after fighting a Big Daddy (they really can take a beating).
The only ways this game is better than Quake 4, Doom 3 or the like is that it's more free roaming (though there's very little use for it), has conversations and some sort of plot twists as well as the light RPG-ness in form of weapon and plasmid upgrades.
The number of choices of approach are quite limited actually, either you shoot them or you.. well.. shoot them. Sneaking past them is usually impossible, or simply just ridiculously difficult opposed to just shooting them and the game has too many scripted sequences where you have to shoot them regardless of how you wanted to do it.
The reliance on scripted sequences for variance is too old, but gives stronger story (scripted sequences are required to have a story, but the use of them outside it is not very good). Some of the things that happened were also very retro FPS-like, for example the one case where I picked up a new gun and swarms of new Mobs were spawned so I could "test it out".
Sad little game in that regard, but can be fun if you ignore all that.
On the confrontation with Ryan, I heard a rather poor explanation for it once (if I remember it correctly, they simply assumed Ryan was raving mad). My own interpretation of it, however, is different.