I played a game or two on the SVN version as mekara, since I never played them before.
They were fun, many cool mechanics.

One time I ended up neighbour to D'Tesh though and had a hard time getting any slaves, that game was fairly well balanced (on hardest difficulty)
But with a "normal" start you just declare war on everybody, and collect slaves by the bucketload. One city and a certain win in the end. Seems very overpowered that slaves are great people. Also that they get part of the bonuses that affect all great people through wonders or civics, make them silly overpowered?
Is that something that has been looked at in the development branch?