My opinion is, that Yamaha has a focus on highly usable user interface. What do I mean?
First, this appeared for arrangers. While Korg PA Series separates modes like Style, Song, Voice, Yamaha offers just one mode, where styles and songs and voices can be played all together. This is one reason, why I decided for PSR against PA arranger.
Now, they carried on this philosophy over to the synth world. Where all synths until now were separating voice mode and multi mode, the Montage and now the MODX offer a mode less operating mode. All patches are just performances containing one or more parts.
In earlier times only voices could use full DSP power. That was the case for early Yamaha synths (I had a TG 500 Module of the SY 55 synth) and is still the case for Korg synths. In multi mode, the effect parameters of only one voice could be used. But now we have enough DSP power to play several voices with full DSP support at the same time. So it was a good decision of Yamaha to eliminate the separation of voice and multi mode. Now we have only performances, and each part of the performance can use full DSP power at the same time.
Another new concept is the super knob. For Korg keyboards, you can control every synth parameter by any keyboard control. This is very flexible, but there is no abstract concept. Now Montage and MODX offer so-called assignable knobs which can be configured to control any parameter of the synth engine. And the super knob can be used to control up to 8 of there assignable knobs at once. So they introduced an abstraction layer they helps to manage complex dependencies.
So I like the Yamaha concepts very much.
