Actually, the R3 is better for traditional keyboard sounds too. That's because it has 64 DWGS waves in ROM that can be used on OSC1 for electric pianos, organs, clavs, guitar, bass, flute, bells, vox, and other complex synth waves. The SH-201 doesn't. The R3 also has 2 multi-mode filters per timbre with a comb filter on Filt2, while the SH-201 only has one 3 mode filter.
Both can do dark/bass sounds. The R3 can do more sophisticated sounds that the SH-201 can't do. The R3 has a huge amount of effects, two insert FX per timbre, plus master fx. The R3 has a vocoder with formant memory.
The R3 has an excellent software editor. Alesis doesn't make a software editor for the Micron (although a 3rd party editor can be purchased). The Micron only has basic waveforms, no ROM-based waves.