To my untrained eye, Chan made chicken salad out of chicken s***.
Our WR depth under Gailey consisted of: Ruvell Martin, Aiken, Hagan, Donald Jones, David Nelson, N. Roosevelt, Easely, TJ Graham, Brad Smith and an unknown Stevie Johnson (in 2010). Gailey made Stevie into a 1,000yd WR. Gailey developed Chandler. He turned Ryan Fitzpatrick from a nobody into a 3,500 - 3800 yd passer. He eventually found the formula and made CJ Spiller into one of the most dynamic RB's in the NFL. Also, there are still 5 OL from the Gailey era that are on this roster - so if Marrone can't figure it out soon enough with the OL situation, maybe he can put his ego aside and just mimic his predecessor.
With our current offense Gailey would make lightning bolts come out of his ars.
Like others mentioned however, Gailey was never able to bring in a D-coordinator worth a damn and those 2010 - 2012 Bills teams had epically bad defenses that the offense was simply never able to overcome. That's what did him in. IMO Gailey was the best offensive mind we've had in Buffalo in a long, long time.