At the center of the redesign is a more specific color scheme - green and blue are for natural features like water and vegetation, red is a specific search result, grey is general ground area, and shades of orange and tan are various types of areas with heightened human activity. This means when you're looking at a zoomed out view of an area, you'll easily be able to pick out the areas of interest, like the Mission District in San Francisco or Midtown Manhattan. The color scheme will also make it easier when looking at a map at street level, where residential and office buildings would remain grey, but businesses or museums would be orange. Additionally, areas of interest are getting a more bold font on the map.
Google said it's going a lot of the heavy lifting of figuring out what's an area of interest with an algorithm presumably based on location data and place reviews, but it is also using a human touch in areas where it's pretty well known what's an area of interest like Manhattan.
The update is rolling out now to the web, Android and iOS.
source: Google Maps blog