I'll cut to the chase: Fahrenheit rocks (aka Indigo Prophecy in North America). Now if you haven't heard of the game at all, I suggest you just head over to Eurogamer and read their excellent (and humorous) first impressions.
I just want to point out some reasons why it rocks so much.
First: adventure fans rejoice, because there is a little bit of every great past adventure game in Fahrenheit. There is a paranormal aspect, with a strong religious/graveyard theme, which reminded me a lot of Gabriel Knight: Sins of the Fathers. A significant part of the game is spent doing police work, and while the obvious origin story there is Police Quest, there are in fact much better ancestors to remember, such as Blade Runner. The movement and camera scheme on the other hand feels like a souped up Grim Fandango. Heck, there is even a tiny bit of Deus Ex in it, and the aspect of switching between characters brought back fond memories of Day of the Tentacle for me. But don't get me wrong, Fahrenheit is far from a copy-cat game. It stands firmly on its own.
Second, though the game is about choice, it doesn't represent itself falsely. Traditional adventure games were known for providing you with tons of apparent possibilities, of which 99% were useless. I'm sure the frustration of reading "That does nothing" for the umpteenth time has shaved millenia off the collective lifespan of adventure gamers when they weren't lucky enough to stumble upon e.g. wear puppy. No such situations occur in Fahrenheit due to the excellent context-sensitive actions. And once you realize this, you'll be glad that the choices you are presented with are actually significant one way or the other.
Thirdly, the action scenes are a blast and a welcome change of pace. Most of them are controlled in a "Simon says" fashion where you follow on-screen button presses. If you make too many mistakes, you fail and your character will usually die. Now though on the surface this might seem like a gimmicky feature, it serves the wonderful purpose of keeping the player active (and thus immersed) even during the most cinematic scenes.
You see, the strongest point of Fahrenheit is not the puzzling, nor the story nor the sound. It's the characters and the way the game puts you in their heads, sometimes literally. One particularly memorable scene has one of the characters suffering from a claustrophobic attack after descending in a dusty, dark basement that serves as an overstocked archive. The view is locked to a narrow first-person view and a mini sidegame of "balance the breathing" is started. However, the main game continues and the player still has a task to fulfill. You will feel the dread and urgency of the character, who wants to get out of there as fast as possible. Lovely.
Another important way that this sort of character identification is implemented is through a Sims-like mental health bar that ranges from "normal", "tense", "stressed" all the way to "wrecked". You will actively start looking around for ways to cheer up your current character so he or she doesn't become suicidal. What at first seems like a gimmicky addition turns out to be a genious move that motivates you to pay even more attention to the environments. It's like a revival of the pixel hunt, except without the frustration.
Though most 'interactive drama' type games that have been made before have always seemed to be films that try to be games, Fahrenheit is more like a game that tries to be a film. It succeeds at both, so if you have some cash to spare, go out and buy it now. You won't be disappointed.
Update: after having played through a second time, and taking advantage of the chapter-feature to replay some sections, my view on the game has shifted a bit. For one thing, the game leaves you with much less choice in certain scenes than you'd think on a first play, because it sometimes takes the 'all roads lead to Rome' approach too strictly. For example, at one point, you are given the choice about which of two detectives should go and question a suspect. Yet, no matter which one you choose, the exact same questions will be asked and the detectives will think exactly the same thing. This doesn't fit their wildly different personalities.
On the other hand, in some areas it has a surprising amount of variation. It turns out that some action sequences in the game are choices in disguise, and by failing them you will continue the storyline in a slightly different fashion. The problem there lies in the fact that such choices can only be discovered by accident. Even worse, the majority of the sequences are not optional, so the game discourages you from trying out too much. Also, I found that by the end of the game (where the most variation is to be found), completing the sequences was a piece of cake so I would only fail them if I did so deliberately.
Similarly, an interesting twist occurred when I deliberately avoided collecting evidence on the murder. But, this is something which you wouldn't think of except when playing the game for a second time. For one thing, at each of the crime scenes, the game prevents you from leaving until you've found a certain clue, so you tend to assume that each possible action is a necessary one. This is further worsened by the interface, where you can only indicate the object you want to interact with, meaning you can only guess what the action is without trying it.
In fact, it seems that the most obvious choices you're given have the least effect of all. The first scene is where the player character commits a murder and is given tons of ways of dealing with it (and which pieces of evidence to leave behind). This was in fact the demo's main (and only) focus point. So why is it that the method of finding the murderer is based on an object you cannot interact with? It would've been much more interesting if you could for example on a second play through, deliberately avoid doing whatever it was that got you caught the first time.
What's also disappointing is that the dialog choices don't have much effect at all most of the time. Asking the right questions simply gives you, the player, some extra information or gives you a slight boost on your 'mood-o-meter', but ends up having no effect on the way the story unfolds generally.
As it is now, Fahrenheit is still a very enjoyable piece of entertainment that does get many things very right. But it could've been even better if they hadn't simplified the puzzling or added some more variation in the main storyline other than the ending. Maybe the guys at Quantic Dream should've played some more Fallout ;).
If you're not a total toddler, you'll remember Commander Keen: the cool 2D platform game starring a boy on a pogostick. With cool music.
