It's a "10" in my book, but I'm giving it a 9 because it honestly isn't a "universal" compressor-- if you want an over-the-top, buttery, super compressed sound, this ISN"T the pedal. It does light compression/harmonic enhancement better than any other I've tried, but it DOESN'T handle a lot of standard "compression" needs so well. (I tend to "hear" compression and sustain as two different things, and this is more of a sustain/enhancer pedal than a typical compressor).
My rig: '51 Broadcaster (or '74 Tele Thinline/'52 Gibson ES-125) -->> Ross comp --->> Ernie Ball volume pedal -->> Crowther HotCake (or Vox Valve-tone)-->> '64 Vox AC30 (or '66 Gretsch Dual Twin/'72 Twin Reverb)
I've owned mine for 18 years (so I'm DOUBLE biased, I love it AND I didn't pay the stupid prices *laughs*). It's the best subtle sustain pedal I've heard, hands down. If you're having noise problems, open it up-- I've had to replace the diode in the center of the board twice, which about every ten years you can hear the noise floor start getting static-y when a battery is in it (nice thing about Ross pedals, when the battery is dead they still operate in the "off" position). I don't know a thing about the electrical reasons for the diode dilemma-- but I know it happens (the diode actually burst the first time-- after months of getting noisier and noisier-- the pedal still worked, but was noisy as hell and the bottom end slowly disappeared).
The best I can describe it's "perfect" tone is that you can play loud, sustained portions of songs without losing any definition to your playing-- chords sound bigger, leads sound clearer, lusher, even with a distortion box. I'm not a big Phish fan, but I can tell for a fact that his super saturated compressed tone is NOT just a Ross Compressor. As some other's have stated, a hollowbody guitar and volume knob is probably 90% responsible for that... The Ross works best for a light sustain or to push the front of a tube amp lightly. For a 'Stones, or early Who, tubey rhythm sound, a Tele through the Ross into an AC30 is impeccable. And kick in a good Tubescreamer-ish overdrive and the sound can make you wet yourself with it's "umpph!" Without sounding metallic or nasally.
Works best with the level high and the sustain somewhere between 9 and 1. Cranked it's noisy as hell, and not very good sounding-- but MOST pedals suck with the settings cranked (TS-808's are worthless with the tone cranked in my opinion).
Raving as I am, I wouldn't hesitate to steer high-gain users away from it-- I've seen some Mesa users here say they love it, but I would not use this pedal with a Mesa, a Marshall, or similar. Nor with a Les Paul (just adds to the funky murkiness I associate with Les Pauls).
For players who center their sound around "vintage" tones, however, and those who use pedals for mostly "subtle" means-- it's a perfect 10!