considering the fact that there are hundreds of thousands of people who play GTA,i wouldn't say it wont sell enough...though it will cause a lot of GTA fanboys (not normal fans,i mean the 9 year olds who yell to their mothers through their mics) to ***** and moan about how you cant get an RPG-7/gunship cheat,even though it's set in the late 40s.
i'm sure that people who enjoy crime movies or stories in general will also like this game,especially since L.A. Noire was featured at a film festival since it was so....cinematic...anyway,you got two large audiences to cater to: gamers, and film geeks.they're bound to sell at least as many copies as they did with Red Dead (5 million units);i mean westerns aren't exactly the topic of many games,and if a western game did well,why wouldn't a crime drama game?sure two different genres,but the principle is the same,right?
(and who knows,maybe japan will release a whole slew of porno games with ultra realistic cleavage physics using the multiple camera motion capture technique they used in L.A. Noire!)