I think the power could use a boost actually. I would say dominate save ends rather than end of your next turn; mostly because our comparison, Ghostly Defense, holds an encounter power in it that is much more viable and fairly potent itself.
I like the idea of it being an immediate reaction...that could be cool.
It would have to either grant the creature another action, or be a save ends in that case. Otherwise this is going to happen
Enemy 1 attacks player 1 /w std action
Player 1 interrupts/reacts to enemy 1, dominates enemy
Enemy 1 is out of actions on his turn, initiative continues
Player 1 takes his turn, end of his turn, the dominate ends.
Just flat out making it a save ends is probably a better idea.