the interface is very nice. Shiny and bubbly in an OSX-inspired sort of way, yet it doesn't really seem copied.
the tiny little rumble as you move your Wiimote cursor over a clickable element is a really nice touch (pun intended). Tactile feedback is sweet.
the speaker in the Wiimote is pretty inspired; now the sound of a tennis ball hitting your racket seems to come right from the racket.
it is amazingly satisfying to bowl or pitch a fastball using real-world motions to do so -- at least until you injure yourself, or throw a 94 MPH Wiimote through your plasma screen.
Gamecube games require a Gamecube memory card to save, completely skipping over the built-in storage the Wii has.
there's no way to return to the Wii interface when playing a Gamecube game. A restart of the system seems to be required.
you cannot close the Gamecube memory card bay door if there is a memory card in it.
it is not at all obvious which way discs need to be oriented when inserting them. Half the time I get it wrong, and the other half I have to give it serious thought first.
if you do insert the disc the wrong way, it doesn't spit it back out. You have to try to launch the game and then manually eject it if it doesn't work.
the Wii system menu includes News and Weather channels that won't be activated until December and January respectively. If you try to use them, the error message only says a system update is required, not that the services aren't active yet. Upon trying to update the system it says there are no updates. It seems to me that it would be more appropriate to have the necessary system update install said channels in the menu at update time, and not taunt us with unworking functionality until then.
Despite the flaws, the Wii truly would have been worth freezing oneself for those agonizing last 3 weeks of waiting for its release.
(I can't wait until some hacker gets homebrew running on this thing, as it would make a truly glorious front-end for MythTV.)
(Imagine a Beowulf cluster of Wii MythTV front-ends.)