I think it's commonly accepted that the GameCube was kicked to the dust when the games that were being released weren't so great... great for nintendo fans, but that's all, and they were dwindling because of the poor quality of the games.
GameCube kept up with the Xbox for a fair while, but then the end of the GameCube's life was just bring out shit re-hash after shit re-hash. I loved the GameCube at the start, and stopped playing Nintendo games at the end of last gen because everything was just so terribly crap. DK Bongo games anyone? Lame.
I also think Nintendo was guilty of trying to falsely bolster GC sales by using lame GBA connectivity as a tool. So many good ideas were touted by never came into fruition because of crap implementation and low cross users. Double Lame.
Essay Pro