I've been playing Bioshock for a couple of days now and it is a great game. It is definitely not for children though! The game is extremely dark and has many 'morally deficient' characters. The sort of people Hannibal Lecter would feel right at home with. The player is frequently exposed to, or forced to take part in, some extremely disturbing behavior and some, let's say, morally ambiguous decisions must be made.
The game mechanics work well and the balance between too easy or too hard has been expertly tuned. If you find it too far one way or the other for your skills you can make it easier or harder from the option panel but I found that 'normal' was perfect for me. The story is well executed but there are a number of plot holes or weaknesses which get glossed over but are easily forgiven. The setting and fiction are very interesting and will keep any avid gamer glued to the screen. The environments are attractive, stylish and immersive. There is little variation in the enemy appearance but their behaviors are distinct and interesting and the AI works well.
If you can overcome the moral dilemmas and psychotic behavior of the actors presented during the game it is extremely enjoyable. It appears there are 10 levels and each takes 2-4 hours to play through depending on how thoroughly you explore each environment. Definitely a game I would reccommend.