And that's why personal opinion is a wonderful thing. The world isn't ending because some people don't like Nintendo as much as they used to. And the world won't end when Nintendo gets a new fan.
I grew up on the NES and SNES. They provided tons of enjoyment, and for me still do. I keep my NES and SNES plugged in, while my N64, Dreamcast, Saturn, and Gamecube switch off on dibs for a plug spot.
I don't see what's great about 99% of the Gamecube lineup, but I bought one and found it a worthwhile purchase (for Metroid Prime and my Game Boy Player). I'm not losing any sleep over someone not seeing what was so great about Super Metroid (but my opinion is slightly biased on this game >.>) or F-Zero, just as no one else should lose any sleep over me or others not being interested in Paper Mario or Pikmin.
Nintendo lost 'it' for me during the N64 era, because Mario 64 got boring after a week for me, and when I replayed it again for the first time last month, it wasn't fun. Zelda doesn't seem like what I enjoyed Zelda for when it went 3-d, and when it went back to 2-d it didn't feel the same anymore. And when you take into account the major loss of 3rd party (which looking back over time is what I preferred over 1st-party) support, that didn't leave much to desire, which is slowly being regained with the Gamecube, but the 2 main 3rd parties I buy games from these days (Enix and Square) have little to do with Nintendo anymore, that is also a dent to the company for me as a gamer.
I don't like today's Nintendo compared to yesteryears. Who cares? I don't let someone's non-enjoyment for what I like affect my tastes, nor should anyone else. If it does bug you, then something is wrong.
Nintendo of today has lost 'it' for me, but that by no means means that when I play an old favorite, 'it' is gone. 'It' may come back, or 'it' may not. I play other systems now also, so it doesn't really matter as much as it used to. Anyway, go generic answer obvious post.