At risk of sounding like I just rehashed the general consensus, here's my two cents...
I agree with the original claim that gaming has indeed changed. We all know that 8-bit systems certainly did not offer top-of-the-line graphics, but it was due to the limitations of the system that game designers put so much effort in creating situations that were more and more "impossible" for gamers, to give them a challenge that kept them coming back. They knew there really wasn't any other draw.
Fast forward to the SNES. Wow, quite an improvement in graphics. Still a bit archaic by our current standards, but seemingly incredible at the time compared to NES. We still saw emergence of good games, but combined with visual draw, things became a bit more enjoyable. Granted, 4 buttons (not counting the d-pad or start/select) made it possible to pull more things off due to the increase in potential functions as opposed to the creative timing needed with 2 buttons, but environments changed to create more challenges.
Fast forward again to N64. Here is where we see a drastic drop in challenge past getting used to the abnormally shaped controller. Graphics were awesome, but without substantial gameplay difficulty, you get flops. What used to be an objective of drawing the player back for replay with challenge and graphics was now primarily graphics, and the more intensive console races made it worse. I'm not saying that N64 didn't have good games (Ocarina, Majora, PD, SSB) but the challenge was certainly gone from most of the games.
GC is still in more infant stages, so we can't make any real analysis until it's age is over.
Overall, I am disappointed with the priority of graphics over gameplay, but that doesn't mean that gameplay has taken that far back a seat with the latest games. I think that we've just been experiencing a time of experimentation and misguided attempts to lure consumers, but it will end soon.