Among the new features for this competitor for your geospatial content exploration and viewing pleasure are a variety of things that make looking at real data more interesting. Most importantly is the accessibility (in the free version of the player) of the ability to use overlays that come from WMS servers. WMS is the standard for sending out pixel-based (as opposed to shape-based) mapping data on the Internet. Although the particulars aren't completely clear from the release notes, this version will allow the use of just about any WMS to provide a content layer. Could this be an indicator that WFS (the feature service that uses shapes instead of pixels) will not be far behind?
Probably the neatest UI feature of the September 13th release is the new timeline mechanism. If you have time-stamped point data, you can use this mode to view an animated window of points as they flow over time, complete with the ability to adjust the window size and see what time-stamp you're looking at. Trust me, my description doesn't do this nifty (and useful) feature justice.
Featured content is yet more stuff that Google is adding in to the slew of items that you can overlay onto your maps.