I've actually been thinking that a setting with all unique races would be interesting. It depends on what races are around, and how they differ from the standard races. Personally, I've never been a fan of races that are like the standard races but only slightly modified. The proliferation of subraces was something I found annoying rather than interesting. On the other hand, I have had fun in campaigns where humans were the only race, and cultural differences resulted in cultural bonuses instead of racial bonuses.
I recently heard about the Shard RPG, which does not have any humans or other standard fantasy races. It sounded interesting from a quick look at the web site.