Nintendo is relying too heavily on its successful past.
Nowadays it seems that the company is relying on the good name that past games have brought them.
Look at the Mario Party series. Mario Party came out in 1999. Mario Party 9 is coming out in 2008. Obviously Nintendo is still making it because people still buy it, but more and more critics are seeing through Nintendo's lack of originality.
Also, look at are the recycled NES and SNES games that appeared for GBA. Why were so many games reproduced?
...So yeah, I think that Nintendo's being too optimistic about reproducing games and making sequels. They can enjoy their current success at the moment, but when consumers become tired of repetitions and recycled gameplay, Nintendo will once again need to come up with something original, like they did in 1985 when they made Super Mario Bros.
...And this is just my opinion. I don't have a Wii, so I don't know what SSBB or Super Mario Galaxy play like.