i had one of these in the late 90s and it is indeed quite powerful - it's a synthesizer as much as a drum machine, meaning it can double as a sequencer or noise generator. i used to program harpsichord solos into it. it can quantize up to 128 beats per bar and can work in just about any time signature you can think of, which separates it from a lot of other drum machines right off the bat. i used to program entire songs without loops by slowing the tempo down. i was unpleasantly shocked to find out other machines couldn't do this...
that said, the flexibility is memory intensive, and there's not a lot on board, so you want to get a card with it (or make sure you can dump programs via sysex).
somebody that used this machine to great effect around 97 or so was autechre. if you want a really thorough demo, that's a good place to start.
www.vintagesynth.com/yamaha/ry30.php
