Targets have long been my favorite quantitative tool for evaluating the potential fantasy impact of a wide receiver. It's quite simple, really; a wideout cannot create his own opportunities. Instead, those chances come as a result of play-calling and a quarterback's reading of the play as it develops. If everything occurs just right, the receiver will have an opportunity for fantasy success. If it doesn't, then the wideout doesn't stand a fighter's chance.
Before you dismiss this statistic, I will grant that this statistic talks purely about raw opportunity. It doesn't delve into how good the throw from the quarterback might be or what the receiver was able to do with the ball once he caught it. As such, it will take your discerning eye to recognize which players have the talent to make something relevant with these opportunities and which ones don't.