I tried the PC Demo three times so far ...
DirectX 9.0 GRAPHICS: 7/10
Not impressive at all, perhaps due to the XBOX360's limitations (which is quite surprising to me). However I've seen much worse before in supposed-to-be recent games like F.E.A.R. when it was released. Most of the textures are blend, almost void of details. One out of tens of examples I could give is when you first enter the lighthouse after the plane crash, before, or after the doors close behind you, just look at the ground texture, it's literally reminiscent of textures I could see in early XBOX games (and I do mean the original XBOX, not 360).
And yes I play with everything maxed, at 1280x960, 95hz, no drivers optimizations, textures at High Quality in CP. It's just blend. And a lot of surfaces are just shiny when there is no logical reasons for it to be shiny ... like Doom 3 for example, like "plastic" surfaces, as if water was on the surface constantly. In my book, and to my eyes that kind of "over-artistic" decision for textures can decrease the efficiency of the atmosphere and situation's believability. And as mentioned the polygon counts seem low on many models, especially "props" lying about on the ground scattered everywhere.
Overall I can say that I was more impressed with Half-Life 2's graphics two years ago then I am with Bioshock's graphics today, especially when you consider that it runs on a so called "revolutionary" engine, and also when you compare it to future games like Crysis. Clearly the Console influence is there, sadly, for us PC gamers to contend with.
SOUNDS: 10/10
Ambient sounds invade my speakers and my headphone in this game, like no others I've seen (or rather heard) before. There is not much to say than the fact that the sounds in BioShock are marvelously crafted and presented (a.k.a it fits the intended atmosphere and feeling of the developers, it makes Rapture sound "Like it should"). It probably has the best sounds in any FPS games I've played in a decade. It might sound exaggerated for some, but I do believe that even just what the Demo has to offer in terms of sound quality, quantity and variety is already worth the perfect score. I can't even imagine what the rest of the game will be like.
ATMOSPHERE: 8/10
It's well done, the level designs forces a semi-claustrophobic feeling in you (well it does for me) as you progress, making you often walk slower to turn that next corner because you don't necessarily want to fight whatever hostile life form might come at you, compared to other mindless FPS games around. I was more concerned to look at the environment and look for what might help me or hurt me for the potential next fight than to actually blindly rush to it like I would in Half-Life 2 for example or even S.T.A.L.K.E.R. (which by the way also has some nice atmosphere going on).
I wouldn't say that the sense of playing in an "ecosystem" is done to its maximum potential, but it does capture a good enough sense that "other things might be going on in that building you're seeing by the window". You know scripts and triggered events make things happen as you move on, on a technical perspective, but the forced feeling of life simulation is present enough to feel like a "living" world more than just a virtual reality of blend polygons and random sounds labeled as a "game". It's definitely better than Half-Life 2's atmosphere, in my opinion, which isn't lacking at all either, and even better than S.T.A.L.K.E.R.'s well-made, well presented world of radioactive, rotten and ruined landscape with death in every corners and trees. BioShock's atmosphere is probably the best you can find in a first-person-shooter in recent years, definitely.
Overall score so far I'd give it around 8/10, 8.3/10 or so, but that's based on the Demo, not the final product, and that's running on DirectX 9. I will need to play the final game to judge new elements of the game such as the story-line, the A.I quality and re-playability potential.