I think in light of the "best NRL player" thread started by Broncoman I have to list Brad Fittler as the most overrated player of the past 20 years :-)
Internation level - Slater (hate on all you want, but he always struggles in the big games for the Green and gold. No doubt he is a superstar at club and origin level tho)
Origin Level - Any NSW half, they always pick them at the wrong stage of their career.. Being picked in the halves for NSW is as good as breaking your leg and never playing again.
Club level - Farah, he is a nothing playing who is made to look good by the players around him.
Is Bronco man setting a test to trap us if we don't agree with him?
Inglis is one of the most powerful ball runners I've ever seen. He's not overrated at all. When he's carrying injuries it shows though.
For me Watmaugh, Hayne (although his is mostly laziness as he certainly has talent), and Cooper Cronk.