O.K. We're not getting into sound right now. These are operational features:

The Korg takes 5-button foot switch, plus a dedicated Damper input and a programmable foot switch.
It has a full row of programmable sliders, plus three programmable buttons just above the joy stick.
It has a joystick, just above the touch strip.
It has a touch strip.
The sliders have 3 modes. One for volume controls of Style, RH 1, 2, and 3, LH, drums, Bass and MP3. Next mode is organ drawbars. Next mode the sliders are fully programmable to do whatever you want. Modes can be automatically select via Songbook or Performance, or manually selected.
It has 3 right-hand voices.
Transpose and Octave change are conveniently located.
You can see the writing. No black on black labels.
It has lots of dedicated buttons. For example Split, Mic Delay on/off, alternate VH settings, Talk . . .
It has knobs to control mic volume, VH volume, amount of effects, double.
It has a light to show you when the VH is engaged.
It has a button to turn the mic off.
It has a slider to adjust style level versus Lead voice volume.
The inputs on the back have labels on the top of the keyboard, so you can see where to plug things in without seeing the back of the keyboard.
It takes a standard AC plug. No wall wart.
It has XLR mic connector.
It has aux outputs and inputs.
It has USB slot on front, plus extra one on the back, plus one for PC.
It has nice touch screen.
It has wonderful Songbook feature. Way better than Musicfinder or Registrations on PSR. It also has Performances, Korg-speak for Registrations. I use them only to have a bevy of lead sounds instantly available, and do everything else with the Songbook. There is a dedicated button to have the Performances change the style and voice, or just the voice.
It has dual sequence/MP3 player. O.K. so I don't use that.
It has a Chord Sequencer plus extensive regular sequencer, plus audio recorder.
You can fully edit, save, replace or delete factory styles.
It has phantom power.
It has Power On setup, where everything you want is saved. When you turn it on it's ready to go.
The Key-start mode is always on! You don't have to hit that button every time you start a song that is not save in Reg.
It has a wonderful Vocal Harmonizer, as good as or better than many stand-alone units.
It has very advanced e.q. and sound enhancement features. MAXX Audio.
It has full-sized keys.
It has Aftertouch.
Every function is fully addressable via midi. Yamaha style controls require System Exclusive messages. Not needed on Korg, but it keeps me from using third party foot switch with the PSR.
I'm sure I'm leaving out some stuff.
All these things are important to me and make playing easier and more fun.
None in itself is real critical, but as a package it is formidable.
Oh, and it is not real heavy. A little heavier than PSR, maybe four pounds. I need the exercise anyway. It is the same size or maybe smaller than PSR! They fit in the same bag anyway.
There are no bad choices these days; it's just that some suit certain players better.