We have feared that the increased definition in the sprites and environments would change too much of Cave Story's unique look, but Pixel knows what he is doing. The new look is more detailed, but still retro -- it just looks like somebody sharpened the focus.
If you haven't tried Cave Story yet, don't worry about waiting for the WiiWare version. Play the freeware game now. You'll be ready to start again when the Wii game comes out.
We're not going to stop talking about Cave Story any time soon. You may as well read up on it and join the discussion!