When you say won't let you, do you mean the game freezes on the load screen or boots you out during gameplay? In both cases, one tactic to try would be resurfacing your game disc. It only costs a few dollars (under 5, typically) and can be done at most local video game stores. A friend of mine had the same problem with Black Ops (he couldn't play Grid or Summit) and resurfacing fixed the problem. To be entirely sure, if possible, borrow a friends disc and see if it runs fine in your console. If it does, then resurfacing/replacing your disc should work. If their disc also fails to run, the problem lies elsewhere. Good luck, and I'm sorry its Nuketown you're missing and not Cracked.
....would be a great game. I really enjoyed both Battlefront 1 and 2. However, the project has been picked up and dropped numerous times by different studios, leaving the status of the game in doubt. If you want to keep up to date on any news regarding its possible development, check out this site: http://www.battlefront3.net/
I find assault rifles such as the Galil, Famas, and Commando to be the most well rounded weapons (best combo of accuracy and damage). The AK74u is also good on smaller maps ala Nuketown/Summit when coupled with either a grip or rapid fire attachment. For Perk 1, Hardline or Ghost is your best bet; I prefer Sleight of Hand for the second perk; and for perk 3, Second Chance is most commonly used. Completing the pro challenges for these perks is key. However, this comes from a player who likes to rush into action; if your gameplay is different, such as choosing to stay back and snipe, adjust your perks accordingly. Find whatever combination suits you best. Good luck.
Gamefly examines your GameQ and attempts to send the best combination based on your list order and the availability of said games. For instance, if you had F.E.A.R. 3 as your first game (with a low availability) and Red Faction: Armageddon as your second (with high availability), they will make every effort to send you FEAR, although more than likely you will receive Red Faction (and so down the list). Once they have determined two games that you have picked and are also available, they will ship the games that day. Shipping time depends on your proximity to the nearest shipping center; for instance, I live in Maine, and the closest Gamefly center is in Pittsburgh, and I consistently receive my games two days from when I've been notified they've been shipped. Hope this helps you.
Yes, you can replay any street crimes by going to free roam for the desk in which the case occurs and locating the mission on the map. Some cases are time sensitive. For your second question, according to the game list, police car 3 is Jack Kelso's car, which you should have gotten through the story, and police car 9 is the Studebaker Commander, which appears behind you after the crash site cut scene in the case, "The Fallen Idol."
The Cerberus Network code allows for some "extras"-the most notable for me being the addition of the mercenary character. I bought the game used, and unless you're going for 100 percent achievements (one of them is directly related to recruiting the mercenary) then a used copy should suffice.