I quite like the class - Duelist-like characters have always been close to my heart, so much so that I crafted an encounter with a Duelist that is specifically designed to be a one-on-one fight (literally, the big guy with the sword in your party is challenged by a duelist to a one-on-one fight to resolve a matter of honor). I also like that Sneak Attack damage counts toward meeting the prerequisites of Duelist, because it always seemed to me like Rogues were meant to be Duelists, especially in Pathfinder, where Finesse Rogue is given as a Rogue talent. I also love the Duelist's Challenge, which seems like the point of a Duelist, but is usually pawned off on some other class (Cavaliers get it instead in Pathfinder--what gives?).

I like how Uncanny Dodge was worked into Fancy Footwork's text, but almost wish that it would be placed on its own as a standalone ability--if for no reason better than to grant Improved Uncanny Dodge to characters who already gain the benefit of Uncanny Dodge through levels in another class (Rogues, Scouts and even Barbarians all get Uncanny Dodge before they make it to Duelist, and get no secondary benefit from Fancy Footwork as such). Alternately, some amendment to the text to account for that (as is seen in the SRD text for Rogue and Barbarian already) might be nice.

I would also make Combat Reflexes a reward for Duelist as opposed to a requirement; doing so would allow characters that aren't Humans or Fighters to PrC into Duelist before level 10 (a race/class combo that offers no bonus feats won't get this until level 9, even if they meet all the other requirements by level 5). A Fighter can still PrC into this at level 6, as can a Human Rogue, but it's not too steep for other characters. It also gives Duelist more of an incentive, though I understand if there are balance issues that arise from that.