Upgrade from Mountain Lion to Mavericks and my iMac got slower I imagine I am not the first one to notice this problem, but unfortunately the update of Mavericks so far have not even addressed this issue.

I have a late 2011 iMac, and while the transition from Lion to Mountain Lion was smooth,  introduction of Mavericks made it gradually, not just too slow, but stack.

Should I go back to Mountain Lion?
That is a matter of personal choice.  

If your Mac is not running the way you expect and this is affecting your work and the use of your computer, I would go back to an OS which served your needs.

On the other hand you may want to persist and find out why your computer is running slowly. 

Certainly there are people out there who have issues with OS X 10.9 however I have it running on three different Macs without too many issues and I quite like it.

For the users of this forum to help you will need to provide more information about what slow means.  What symptoms are you experiencing?  What is the configuration of your iMac - which one is it? Processor, memory etc.