He's pretty good. Turned out much better than I had expected. Depending on what you need, Gallade can be pretty useful, but you have to worry about his weak Defense stat. More than once I felt the burn of his base 65 Defense stat; even when taking a not very effective Rock Slide, he'll sometimes go all the way to the yellow, easily within Revenge Killing range.
So yeah, I'd say Gallade would be a great addition to your team, just work on a workable EV spread.