I bought this synth because the original model (the one with a keyboard) was frequently praised for its clever UX, powerful sound editing, and the stock presets. The commonly-cited drawback was the keyboard itself, as it was fairly limited, and not especially well-made. The rack version solves this by letting you plug your own MIDI keyboard, which I did.
I'm definitely not an experienced synth player, and while I've worked in some FM VSTs, like the Native Instruments FM8, I won't pretend that I usually know what I'm doing. As such, I sadly can't go into a lot of depth here. What I can say is that this synth is attractive, and reasonably-well built. It makes FM synthesis fairly approachable even to people like me, and the 256(!) stock presets cover a wide range of classic and experimental sounds.
I'm not a classically-trained pianist, and if you are, you'd get a lot more out of this than me: an experienced pianist will be able to fully leverage the nuanced dynamics and complex velocity layers of this FM synth. It definitely benefits from a proper keyboard, and the rack version makes a lot of sense. This said, even if you are like me, with a 'John Carpenter range' of simple one-handed melodies, you'll love the Korg for its clear, controlled tones, and intricate layering of parameters. You can tell how much effort the R&D team put into this instrument, and it feels like a labour of love.
There are the aforementioned presets to get you started, but it's not hard to start working on your custom presets. The built-in sequencer is good. The drum sounds will put most drum machines to shame. It also has a 'Random' button, to help you come with ideas, and even takes DX7 patches (although apparently they don't quite sound the same on the Korg).
