"1. What does noire mean or what does it refer to?"
Noire (feminine version of Noir) is french for black and refers to a genre of films usually crime related that deals with corruption, violence, sex.
"2. Is it really open world? I heard the map size is bigger than gta 4's and rdr's combined or something."
The map is 8 sq miles. It is open world but it is not a sandbox game. You will be able to roam around but outside of random small crimes (like muggings and small robberies) there isn't going to be alot to do outside of the cases. There aren't any sidequests, there aren't any mini games and you can't run around shooting civilians.
"3. Is this going to be another heavy rain or alan wake where you solve clues?"
It won't work like heavy rain where it is more like watching a movie. You will have full control of your character as you move around the world and you can investigate the case how you want (finding evidence, deciding which leads to follow, who to interrogate, and how you react to what they say during interrogation) It is much less controlled than heavy rain but it is focused on interrogation and investigation with action such as shootouts and car chases only when necessary for the story.
"4. Am I the only one who gets the feeling the story will be predictable, like at the end, the police department are actually the main bad guys?"
I don't think the story will be to predictable. Writing detective stories is tough to begin with and considering the amount of praise the writing and dialogue has gotten they have done a good job so I have alot of faith that the story will be well done.
I refuse to take this signature down until the 49ers win the superbowl