LBP first 3 weeks: 598K
LBP next 3 weeks: 375K (63%)
LBP next 3 weeks: 550K
Seems nice, but LBP launched late October. Let's look at some possible comparisons.
Fable 2
First 3: 1490K
Next 3: 292K
Next 3: 390K
Fable 2 also has very good continuation in sales, but not quite as good as LBP (excluding first 3 weeks, LBP has sold 243K more. That is ~ 1/3 more).
Far Cry 2 (Ps3 + X360 combined)
First 3: 730K
Next 3: 296K
Next 3: 530K
Far Cry has about as good continuation as LBP (too close to tell a difference).
Saints Row 2 (launched 1 week before)
First 3: 983K
Next 3: 243K
Next 3: 344K
Saints Row 2 does not have as good continuation as LBP.
Fallout 3 (launched a week later)
First 3: 1423K
Next 3: 539K
Next 3 (estimated): 760K
Fallout 3 has slightly better legs than LBP. This is across both versions, but if you count the 360 version only..
First 3: 916K
Next 3: 350K
Next 3: 530K
That version (alone) is doing on par with LBP.
So LBP is doing slightly better than the other high-profile HD games this year. It is really to early to call (and LBP bundles might skew it a bit)
For last year, there was only Guitar Hero 3 from the same time-frame. Let's check the X360 version. It was released 1 week after LBP.
First 3: 901K
Next 3: 425K
Next 3: 546K
(Next 3: 221K)
So that one actually did a bit better. It ended with almost 4M.
LBP could end around there (unless bundles take off like heck). Of course, it isn't certain LBP will do this much. I'd put it at (non-bundles) 3-3.5M.
It is legging slightly better than most HD games, but not a lot better.
So LBP is legging