The main thing that gets to me about any overdrive pedal I've ever played is the lack of top end detail and response, compared to a good amp's natural (or channel switched) overdrive. Only really talking about the real light, gritty, chime-y 'just pushed' blackface kind of sounds here - below Tubescreamer levels.
Recently I spent a good half an hour switching between a certain 'poor-man's-Klon' pedal (I'll get lynched if I mention the make!!) and the middle channel of my Twin with a Tele. Forgetting about the EQ differences between the two, the amp's overdrive was just a bit more responsive, with more detail, sparkle, and 'air' in the sound, which was obviously more noticeable the higher up the frequency you listened. The Fulltone OCD, D*A*M and Colorsound pedals I tried at the same time all had the same issue, no matter what was done with their tone controls. I guess at the end of the day this is, IMO, what makes a pedal sound like a pedal (in a bad way!).
So if someone could invent a light overdrive pedal that doesn't sound like what it is (a pedal!) then I'll be happy!
While I'm on the subject.... why have so few companies made pedals with control knobs that when turned all the way off or on, click into a different mode/feature? Like the Fat Boost mentioned, or the "Klon" type pedal used above that switches to a clean boost when the gain is wound all the way down? Or like one of the new Orange heads or the Matamp GT1 which both have master volumes that click to off/bypass when turned all the way anti-clockwise.
^ Someone should do that for the tone controls on amps - each control could be clicked to 'bypass' when wound totally off, giving the potential for 3 different levels of gain boost without any other visible knobs or switches...
