In addition to showing most popular free and paid apps, Google has added categories to surface top new free and premium apps, and the most downloaded over time. The charts are also now localized by country. To keep you ahead of the curve, the home page has a new section featuring trending apps.
Google also follows in Apple's footsteps by highlighting editorially chosen apps in the mid-section of the Market site. This is in addition to the carousel and tabs for featured apps. Google will also reward those it deems its top Android developers, with an icon to help them stand out.
The recommended apps section has also gotten work done. Once you've clicked an app, WorldMate, for instance, you'll see lists on the left for apps that others respectively viewed and installed.
I have two thoughts on this. First, Google's changes are very simple. With the exception of the editorially-selected apps, Google's new lists lean on what the information giant does best--using its considerable data to reflect which apps and developers are making it big. As far as I can tell, there's no advanced algorithm to suggest apps to you that you might like based on your current collection. Maybe that'll come later.
Second, and also excluding the editorial category, the new lists won't release Google's app store from the usual paradox of discovery--wherein popular apps become more popular because people see they're well-liked on lists, and little-known gems often remain overlooked. I might like to see a list of users' high reviews for a variety of apps. I'd be more inclined to try a new app based on an thoughtful or amusing write-up, rather than on total download counts alone.
At any rate, the changes are live, so you can begin taking advantage of the new lists and categories right away.