Which race is the hardest to play and why?

[chrisdcoulombe]

For me being isolated is the hardest, no matter what you I'm playing.  That is probably one of the reasons why playing a mul, a sorcerer, a mind bender or a void cleric is considered difficult. 

I don't really find elves difficult to play so long as there are other elves around to interact with.  Especially rinth elves because you feel the pressures of the rinth and the discrimination, which helps bring you into the xenophobic mind set.   

Dwarfs aren't difficult for me either because you can have safe interaction.  You can justify anything as a dwarf so long as it is bringing you closer to your character's goal.   

Half-elves are harder than Humans, elves and dwarfs, but still not incredibly difficult.  Following the docs there is still a huge amount of flexibility.

[Fujikoma]

I think if I played a mul, I would loosely use the monster from Mary Shelley's "Frankenstein" as inspiration...