The Android Market is looking to start over, the apps will stay the same but the look and feel will give the Market a complete overhaul of it's current state.
On the home screen of the Market there will be a new carousel feature that allows users to flip through apps in a "Cover-Flow" style look. There are also new categories "Live Wallpapers" and "Widgets" and there are promises of more categories for popular apps in the future.
Once inside an apps' page there will no longer be the old tabbed interface but rather a single, "streamlined" page. There's also a heavier use of the color green.
Google have also changed the refund time of apps from 24 hours to 15 minutes and they've also increased the maximum download file size to 50MB with the hope of richer games and offering better support for different screen resolutions, etc.
This new update to the Android Market will begin rolling out to Android 1.6+ users in the next couple of weeks.