1- Obviously its a game based on the Streets
2- Should it have Police?
3- Should it have Typical Tuner Cars?
4- Should it have more Race/driving Modes?
5- Should it have a Free Roam Where you go to the race you want to attend/meet friends online etc..
6- Should it have a huge variety of Customization?
1) Yes, it should be based in a huge city with thousands or perhaps even millions of circuit layouts possible (With maybe a circuit creator)
2) I don't think it should have the police. I had a lot of fun in U1 and U2 because it was all about the racing and improving the car. In Most wanted they dumbed down the other parts and added Police which made the game less fun as you were restricted in free roam by having to escape the police when you were actually just on your way to that tuning shop. It meant you had to fast travel everywhere, which sucked some of the immersion out of the game.
3) Typical tuner cars are the heart of NFS games. I don't want there to be huge differences between the cars after upgrades. It seems as of late NFS has the trend that the exotics you get towards the end are the best in almost every way, and you struggle in the races if you don't have one.
4) Circuit, Sprint, Drag, and possibly Drift. I also liked the races in Underground 2 which were off the streets like at a makeshift circuit in an airport or something. You don't really need any other race mode. I hate speed trap events or whoever gets the fastest sectors wins, a race should not be decided before the finish line.
5) Free roam should be there, but fast travel should be an option for those who dislike the feature. Someone mentioned random races with others you meet on the street would be good (I seem to remember a sort of cat and mouse minigame in Underground 2 or Most Wanted, where you can challenge people to catch you or vice versa). Combining this with online would be good, but it should be available in it's full form offline aswell.
6) Yes, of course. I want to be able to customise anything and everything. Not a big fan of having different manufacturers for parts though, this always confused me in NFS-U2 because it didn't specify whether or not there were any performance differences between them.
Oh yeah, and the game MUST be at night. No point in Neon lights during the day