More singing sustain than fuzzy distortion. Truly beautiful sound. The bass knob is missing on many overdrives, but is essential because as the gain is increased, so is the bass. With the bass knob, you can roll it off when the pedal is engaged. I always thought that great tube amp distortion had more to do with saturating the output transformer than overdriving the tubes and this pedal confirms that. Of course, it does it by saturating the Neve transformer. At lower gain settings it's great for R&B and blues. With the gain all the way up, any Led Zep song sounds fantastic. I use it in enhanced mode all the time, which produces more harmonics. Not great for ultra metal - there's not enough gain and it's too sweet of a sound. Best overdrive I've ever heard - and I've heard a lot.