You mean for the Mac? I didn't think 2013 was available for the Mac, just the 365 which contains 2011 but uses a subscription model.
I did buy 2013 to run in my Win 7 in Parallels. I haven't used it extensively but from the little I've seen it has small but nice enhancements that improves some common tasks (e.g. adding a row or column to a table in Word) and cosmetic changes to the UI's look and feel.
I expect my experience is familiar to others' experience.
There isn't anything "wrong," per se, with iWork, but for someone like me with a job that is highly dependent upon features in Excel that Numbers does not do, Access databases, and twitchy/particular templates in Word that don't always migrate to iWork, having Office in my back pocket is a necessity. I currently have Win8 and Office 2013 running in a Virtualbox VM (mainly because I moved the VM from Linux Virtualbox and my attempt to port it to Parallels 8 was unsuccessful).
I prefer iWork for all of my personal work and volunteer organization work. I've used iWork from day 1 that it was available.