Fabulous walkthrough of the Zune on-board interface at Engadget. It’s a bit over 13 minutes long.
Hmm... Wireless. Big Screen. Clickwheel. I'm thinking: mobile multiplayer Quake.
While it may look like a clickwheel, the Zune "only" has cursor keys; there is no touch sensor that allows navigating the device by "rotating" the "click-wheel" in iPod style.
That shouldn't have too much of an impact on playing a (potential) Quake port on it, but I'm really curious to get my hands on a Zune and see what controlling that player generally feels like. If the Engadget movie is any indication with all that button-tapping going on, I wouldn't be surprised if the iPod's "all-you-need-is-your-thumb" click-wheel approach felt faster and more comfortable.