NES didnt really have a direct competitor, per se.
SNES had Genesis so that cut the sales down obviously
N64 had the PS1 and for a short time the Saturn so with the rabid success of the PS1, that cut it also.
Gamecube has the PS2 and Xbox to deal with and well...the fact gaming has gone inanely mainstream thanks to the PS2 and Xbox
Thats my excuses for Nintendo's dwindling sales
