Oh... graphics?
Yeah... that's been what's going on.
You see, when 3D came into existence... people were amazed and in awe...
But when good gameplay appeared in 3D, people were astounded.
Then 3D became BETTER 3D. PEOPLE WENT BANANAS.
It happened around mid-Playstation.
When Playstation hit a graphics-mark people haven't seen normally, the gaming industry took notice at the sales for better graphics.
The gaming industry also noticed that people tended to avoid bad-graphics, even if the gameplay was beyond fun.
That's where the gaming industry split.
Playstation headed for graphics.
Xbox tried to show off its PC-esque capabilities (which included graphics).
Nintendo still aimed for gameplay.
And SEGA... well, they were unfortunate. Too soon, SEGA, too soon.
Playstation had awesome gameplays in upcoming 3D games, but if you really took notice: The gameplays were becoming more stale as the graphics got better... it was the same thing over and over, even though the systems could handle better controls and action-sequences. ( Good example: Kingdom Hearts gameplay... though fun to most of you, you do realize that it could have been 100000x better, right? ...or do you not remember old games? ...or are you just blinded by the fanfiction and colors? )
Xbox... well... they're Xbox... they're like PC gaming: Add more features, add better graphics, and add even more options--- but they tend to skip out on gaming. All their genres follow a certain formula that they think they've perfected (but that's not completely true)..... henceforth, it feels like all they focus on is graphics, but really, they've never really been top-notch in gameplay. -Not saying it ain't fun, just saying that they aren't that innovative in controls.
And Nintendo kept following the same formula they always had. The sad thing is, Nintendo didn't really care about graphics... they thought gaming hasn't reached its potential in gameplay yet, and thought the gaming industry was too focused on graphics- of which they could have worked on anytime. So as truth shows: Graphics has gone to the gamers... most gamers tend to hate the Wii because of its "old-gen" graphics and unfamiliar gameplay.
But Wii's paved the way for the other systems... the other systems' companies realized how much of a "threat" the Wii was, and started planning on future console controls.
Gameplay doesn't suck nowadays, it's just not new (except on the Wii side)... sure, we get more options and more graphics - but whatever happened to a good ol' fun-time with family like we used to have with the old Nintendo? (I remember constantly playing Super Mario Bros. 3 with my family all the time)
Gamers have kinda' burned that path a long time ago ( when their parents told them that video games were from the devil

), only new gamers and loyal Nintendo fans still appreciate that kinda' thing.