It responds very much like the volume knob on your guitar, turn the level and drive down and you get a very warm, tube-like overdrive .. but crank that baby and you can sound like Hammet, Dimebag, etc.
It's a very versatile pedal. I played in a very loud, heavy progressive-rock band back in the early 90's .... lot's of drop-D tuning, etc .... and my Tube Screamer gave me all the crunch and gain I needed .... later on , I joined a more "classic" rock band .. Stones, Hendrix, etc ... and the Tube Screamer adapted perfectly with a few adjustments .... now, I'm getting more into Traditional and Texas blues .... and the Tube Screamer is still my only choice.