Though Nightfall has the potential for some really awesome loot, it's not often you will get an exotic out of it. I do the nightfall three times a week on three characters and every now and then I get something cool but more likely than not it's something I don't need or already have. The real reward is the 25% boost to reputation and experience earned. This is invaluable for leveling gear and weapons and boosting faction rank if you need it.