Transparency. I like to still hear the character of my guitar & amp through the pedal. I want a pedal that just distorts/overdrives, but doesn't add or scoop midrange. I'd like far less compression than you get with a Tube Screamer type effect, and more gain.
Currently I am using a Boss BD-2 Blues Driver. It's very close to what I want, but the decay on chords is kind of splatty & fizzly with some settings.
Build me my pedal. We shall call it The Bonafide.