While the modder in me rejoices that we can have unique improvements, and the immersion gamer in me smiles at the stylishness of the Terrace Farm, the powergamer in me cringes to see that they are so utterly, utterly bad. Along with pretty much everything in the DLC.
The only thing that has some merit is the Inca UA. Movement bonus in hills is nice and a bit less than half tile improvement cost is a bit better than Harun's ability, so overall it's an ok package assuming that Inca start in rolling hills.
Spain remains to be seen, they get pretty big bonuses in the early game with extra gold and happiness from natural wonders and they probably actively seek to settle near them. Their UU are mediocre, though, and don't compensate for the fairly weak and situational ability.