I think the bigger question is when one is 'disappointed', compared to what expectations? 1st week sales are like box office sales for 1st week for a movie. It may have some predictive value for long term sales. Thats about it.

To me when looking at 1st week sales, I think a more accurate number would be to look at sales numbers as a percentage of user base. For example, U2 would have a 1st week attach rate of 3.2%. The problem with U1 is that it was released at different times, in different regions, and it was not front loaded like U2 (U1 had greater sales week 2 and week 3, and then went down) because the the game was not hyped and marketed like U2, and word of mouth increased sales. But if we look at week 1 sales in US (which is where it launched 1st), the attach rate was 1.3% (it goes to 2% in week 2). Factoring in that sequels on the same console traditionally do not do as welll, I would say that U2 is certainlly not a disappointment compared to U1. The difference being that U2 was definately quite front loaded, I suspect that U2 will end up with similar total sales as U1 (as that game sold well long term because it was not front loaded). If you compare U2 to games on same console, then look at % again (KZ2 was at 3.4%, thus sold better than U2 based on console base, but pretty close).

If one is 'disappointed' in sales because one is comparing to the other console, then that is the problem of Sony and Naughty Dog for being console specific and not multiplatform. Most of us would agree that if the game was on the Xbox, it probably would have had 2-3 times the sales in 1st week, but that is directly proportional to the fact that Americans like shooters.

Don't even bother comparing with Halo 3 as the % on that game was 32% (3.8 million sales on 11.7 console base). NO game will come close to that (because the console base was low). MW2 has a chance at beating total sales, but not based on consoles user base.

Gran Turismo is the Halo of racing games, and its sales prove it.