m0zart brings up a good point: system power is relative.
Even the very best games for the 360 do not represent a huge leap forward from the original Xbox (I'm gonna get flamed for saying that, no doubt). While they certainly justify having the system, they don't give me the "holy crap" factor that upgrading from a NES to a Genesis or SNES did.
I view graphics advances like this (hang with me on this analogy): If you are obese and very out of shape, small changes in lifestyle can create some very dramatic results. If you are already in great shape, it takes an extreme amount of hard work to improve. What one has to do to go from, say, running a mile in 18 minutes down to 12 (which is what a fit adult should be able to manage) is pretty basic. What an elite athlete has to do to go from a 4.1 minute mile to a 4 minute mile is rather extreme.
In video game terms, the difference between an Atari 2600 and the next generation above that were relatively smallish (compared to the advances we see now), but the Atari graphics were so primitive that small upgrades in hardware equaled dramatic differences in the on screen visuals. Shoot, there was even a dramatic difference between early gen and late gen Atari games on the same system, as more games were developed with hi-res graphics.
Now that we've come as far as we've come, however, it takes a system that is literally a super computer being sold at a loss to give us what one could say is only a relatively marginal boost in graphics, gameplay, AI, etc. Yep, I'm very happy with Gears, Oblivion, Fight Night etc. but I see where "a" is coming from here. Oblivion isn't really that much different than Morrowind, other than it looks better. Fight Night plays the exact same way as all the other Fight Night games. It just looks awesome. I also didn't notice the better looking character models in Madden 07 act any smarter than they do on any other version of Madden.
Huge technology leap. Small gains in gameplay. Therefore, what the Wii does is very significant: it takes the one aspect of gaming that has been relatively untouched since the NES gamepad: control. Since we haven't fundamentally changed control in the same way we've changed microprocessors and graphics technology, we can have a huge leap in gameplay. This is what makes Wii significant, important, and worth owning.
Listen, my comparision breaks down because, to people who are a bit myopic in their gaming tastes, yeah, Gears, Resistance etc. are going to seem light years ahead of anything ever put out on Xbox. They will say "that's crap Rob, the difference between what I can play on new gen is so much better than what I can play on an Xbox or PS2!"
And I'm in m0zart's boat, both systems have great value and I'm a happy owner of both. I am just trying to shed some light, or append, a's argument. A is thinking in the macro, when maybe some of you are thinking in the micro.
-Rob