Having just played with a prototype for a few minutes, I'm really impressed with the Zune HD. I've got a video, too, showing off how well the animations work.
The device is tighter and more physically beautiful than the iPod Touch and it's got a better UI, the main menu's scrolling so natural through the swipe gestures. There's a little note on the side, under the volume toggle—"Hello from Seattle." The power button is up top. The home button is nice and prominent, a bar rather than a round button on the Touch. It's smaller. And the accelerometer is more swift in responding to repositioning; images rotate very fast.
Of course, this thing won't have hundreds of apps ready for download when it comes out, as the Touch does.
But I would take this in a heartbeat, provided they get around to making a Mac client.