It looks pretty good but I think the Dark Hexblade's Curse could actually stand for some more power. Perhaps remove the blindness effect and instead add...

"On a failed save all of the normal penalties for the curse and the Unseen Curse may completely paralyze either his target's arms or legs. If arms are chosen they lose the ability to use move their arms, in other words wielding weapons, wands, staves, rods, casting spells with somatic components, getting spell components, and any other task requiring the use of hands becomes a futile and failed attempt. If legs are chosen the target's speed drops down to 5ft. and they lose their Dex bonus to armor class for the duration of the curse. These effects last for a number of minutes equal to twice the Unseen Blade's Charisma modifier."

It makes the tenth level of this class a lot more appealing then permanetely blinding someone, which is the equilivant of a 3rd level spell usable as many times as the curse.