It always depends on what you deem worthwile, the payout isn´t much different from the likes of adsense. But there are actually different reward models.
PPC = Pay per click, basically what adsense does
PPL = Pay per lead, you get paid if the other person does something, like registering for a newsletter (or to a different game)
PPS = Pay per sale, you get paid (usually a percentage) of what the person buys.