Office 2007 changed file formats to OOXML, and also expanded Excel sheets from 64K to 1024K rows. That helps me a lot; 64K was way too small.
I'm not sure what meaningfully changed later. In 2014 I bought Office 2010 and still use it; 2013 didn't seem any better and I think a couple of things were reportedly worse. And I still don't like the ribbon.