Worth the money? Depends
I've been using it for a month or so now, and while there aren't a huge number of staggering new features the changes they have made do make it a smoother and more pleasant experience. 2013 is definitely something that benefits a business buying fresh now or a subscription user (what they would prefer you to be anyway). Since businesses often skip a generation anyway the difference from say 2007 is far more enticing.
Here are some new bits not mentioned:
- Animation on cursor movement, selection boxes etc (sure eye candy but nice)
- Cleaned up visual style gives more document room (YMMV)
- Themes and styles cleaned up and made a bit more consistent across the suite
- Proper presenter mode on PowerPoint
- Better online template integration
- Better document navigation in Word
- Outlook has better meeting controls (although somebody in this thread didn't like it)
- A lot of annoying bits & pieces - inconsistencies cleaned up (for example social connector and Hotmail access in Outlook).
- PDF tools
- One big negative you can't publish your calendar to office.com you have to find another provider to sync to (I went with icalcx.com)
I'm sure there is lots of other cool stuff I've not played with (certainly Excel seems to have had some love lavished on it to make things easier). Is it enough to force you to upgrade maybe not but if you have a subscription you'll appreciate it.
P.S. Not part of core Office but Visio finally properly acts like an Office application - and definitely is a worthy upgrade.