Is the xd dx hack worth playing over original gale of darkness?

Depends if you've played the original. If not, play Gale of Darkness first, the hack is tuned for people who already know it. What these hacks do is make the game harder and widen which shadow pokemon show up, which only lands if you remember what the vanilla version looked like. If it's a replay, go for it, the extra challenge is the whole point.