I'd suggest taking your own headphones next time, for starters. A lot of them sound like
$#@! Good ones will tend to give you a pretty fair picture of what you'll get on tape. Korgs tend to sound pretty rich out of the box, so whoever let you demo it wasn't on the ball at all! Korg also "ports over" many of their better sounds when they make a new model, so I'd be surprised if they made a stinker these days.
A lot also depends on what your end use will be and how much programming skill you have. Usually, a few minutes of tweaking will bring a lot of the current sounds into line with your tastes. A little filtering or a slightly longer envelope can often make it ring the bell. I suggest you give it a 2nd try in any case; its always good to sleep on it and go back later, which is true of ANY audio experience.
"Punch" can be a matter of simply knowing how to sharpen the factory sounds here and there. My 01 didn't really have a great piano in the presets, but when I combi-ed a pair of them with a bit of string bed in the background, it sat up & roared! Give it another listen & THEN decide.