An amazing environment with great gameplay, an overall awesome experience.
The first thing you'll notice about Bioshock is the fact that it is absolutely gorgeous. Every model is highly detailed and superbly textured (with next-gen shine!). This is quite a feat when looking at the high number of things that are spread throughout the world and they all tie in so great with the entire environment. The game puts you in a 60's style city, Rapture, and everything really feels like it's straight out of that era. Even the weapons tie in which really keeps you feeling like your part of the game and holds to the realism of the entire thing. It may seem like a city built under the water wouldn't hold much of a realistic feel to it, but it's about the city itself not it's location.
Throughout the course of the game you never leave the city of Rapture (once you've entered it) yet it never forces you to backtrack a ton and you're constantly finding yourself in totally new environments. Completely unlike a game like Resident Evil (1) which puts you in a mansion that you travel through the same parts over and over (no matter how great a game it may be, the backtracking can get painful). You'll explore all different parts of Rapture and constantly be finding new things.
The exploration in Rapture is really the best part of the game. It's really nice to see so many rewards for exploring around because FPS games aren't usually known for this, even RPG's can have poor rewards for exploration other than you gaining levels from doing extra fights. Bioshock gives you real physical rewards in the way of money, invention items, plasmids and more. I found myself often wandering around for an hour or more when I entered a new area just to check everything out. Granted this isn't required by any means, the rewards really are worth it (especially if it's your first time through the game).
The game features an excellent array of guns, I had a blast using all of them equally even though the cross bow was my distinct favorite. They all have a great feel and I found all of them effective, even the wrench and handgun they give you towards the beginning. Each gun features 3 different types of ammo and can be upgrade twice at machines hidden throughout Rapture. I think you'll find that they each have a unique feel that make them stand out from your standard array of FPS guns.
The game's sound was top notch as well. There were always little things going on and the AI was always doing something in it's own world instead of just walking a set path back and forth all day. The Big Daddy's and Little Sister's are the most impressive to watch interact. The Little Sister's are always having a conversation of sorts and the Big Daddy is always displaying such signs of protection it's really interesting to just watch.
Now, I have to point out what I saw as downsides to the game. First and foremost, the end of the game got fairly buggy for me. There were little things throughout the game like floating objects, but towards the end the sound really started to get messed up. At times I wouldn't hear any sounds when doing certain actions or it would be really quiet and once it even got stuck in an endless loop that forced me to restart my console.
The other things I was disappointed about was the fact that the game had some awesome features like inventing that were never really needed. There were a few times with inventing in perticular where you had to make an idea to progress the story, but for the most part I found so much ammo around other places that I never had the need to invent it. I found myself inventing useless items just to get my invention achievements. I also didn't find much need for all the optional ammo types that were given to me.
However, the game presents so much good that these downfalls (besides bugs) are really minor. It's nice to seem them there and have them for the player if the player chooses to use them, although it would have been nice to feel like they had a definitive purpose. Really though, the game is great. An outstanding shooter and a game to go down in the history books. Don't miss the chance to play Bioshock as I know so many people already haven't. You won't be disappointed by any means.