From my research in trying to pick out a speaker amp, MOSFET/JFET amps tend to reproduce that tube magic while retaining many of solid state's advantages over tubes, but there are still things people say tubes do better, and there are things FETs do better. The best FET based amp I know of, the Firstwatt SIT, has gotten rave reviews but always with a caveat that while it does many things better than tube amps, tube amps still have their own advantages.
Granted, the guy seems to be a bit of a pessimist, but his point does seem to be in common with a few other's opinions I've read.
Another review stating the differences between the SIT and a SET amp towards the middle-ish.
And here's the RWA Sig 15 being compared to an Audion tube amp near the end of the review. There's a more explicit review on the website comparing the RWA Sig 30.2 vs a Trafomatic SET, but IIRC the 30.2 technically isn't FET based.
So basically, I'd say MOSFET/JFET based designs have their own unique category of sound that can appeal to a lot of people, but tubes still have their own appeal unique to themselves.