It won't outsell Halo 3 imo.
1. Halo 3 was end of the trilogy and Reach is prequel. I just don't see same kind of enthusiasm within mainstream audience for prequel as for last game in trilogy. '' Finish the fight'' was pretty catchy phrase.
2. This time around it has a lot more competition than in 2007/2008. Call of Duty is even bigger series nowadays and it will get new entry this year (pre-orders currently are outpacing MW2 and Reach) and Medal of Honor that also have nice number of pre-orders and EA will definitely put a lot of money to advertise it.
3. Second entries for already established franchises on consoles tend to sell less than first entry. See Final Fantasy PS1 and PS2 gen, Metal gear solid last gen, GT last gen, Super mario galaxy 1 and 2 this gen etc..
Of course I can also be wrong. It will defininitely have bigger opening than 3 though. Probably next year we will see which side was right with ltd.
