I liked his tone, though I didn't particularly dig hearing it cloned, often poorly, all over the place.
But really, it's not even correct to talk about Jaco's "tone" as if he had only one. He didn't just have one tone, he had toneS. That by-now cliched back PU close to the bridge sound was only a part of what he did. Part of Jaco's greatness was actually the way he was able to wring different sounds out of his instrument with variations of touch and hand position. He had a sophistication in that regard that relatively few e-bassists up to that time had shown (and not all that many have shown since). If you listen to his recorded catalogue, or watch videos of him, you'll see what I mean. The sound he got on funky 16th-note stuff was different from the tone he got on melodic fretless ballads, and both were different from the tone he got when walking on stuff like "Fast City."
From seeing him live several times and hearing most of what he recorded before falling off the deep end, I think his sound actually had more low end than it is often given credit for having. When properly recorded, that is. I think some of the records he appeared on, even some of those he's most famous for, were actually not recorded all that well with regard to the bass, heretical though that may be to say (perhaps in part because some engineers didn't deal ideally well with bass sounds outside their usual way of doing things? I dunno). For instance, I think his bass could have been rendered better in the ensemble pieces on his debut record; it sounds more lightweight than his real sound to me. And at least one of the Weather Report records is inexplicably bad-sounding. On their second eponymous record, the one with Volcano For Hire and Dara Factor Two on it, both the sax and the bass sound just terrible--midrangey, honky, and dull. OTOH, I think Jaco's bass on the Joni Mitchell records sounds just beautiful.
