I purchased a used RS-5 recently, and I have to say that this is a pretty decent synthesizer. It has some nice features that took me by surprise. First, it has an arpeggiator with a number of interesting patterns. Second, it has a nice time-slicer to give chords a mean, rave-like effect. Third, it has a decent sound set with nice, airy choir and string sounds, plus a number of excellent sound samples (like wind, cars, ect.). Finally, it has three different effects processors to really shape the sound. I don't believe that it is the top synth on the market, but it is a decent synthesizer with good sounds.
I would recommend this to a professional musician who needs a top-of-the-line sound set and every feature imaginable.