I bought The Legend of Zelda: The Wind Waker used a few weeks before I got the Wii/Twilight Princess, and played it a bit and enjoyed it. But then I got engrossed in Twilight Princess and the Wii and hadn’t played Wind Waker since. Just yesterday, I started playing again, and I am on the fence as to which Zelda game I like playing better! Wind Waker is really cool because the cel-shaded graphics are amazing. I love the style of it so much. I haven’t seen any other game look like this. Also, the overall tone is more light-hearted than Twilight Princess. The dialogue is funny and the characters (especially Tetra) have a lot of personality, and even some of the actions, like hiding in barrels or sidling up to a wall, are fun and childish (in a good way). It’s a nice contrast to the more “serious” tone of Twilight Princess.
Lots of people who got a Wii and are new to Nintendo games ought to get Wind Waker. It’s really one of the best Gamecube games out there. I just wish I could use the Wiimote and Nunchuk with it. Since you can pick up a used copy of Wind Waker for ~$15, it’s really a no-brainer!