Chuck's spot on.
After building this and monkeying around with the circuit a bit, I have a couple tips.
To get closer to what you want, you need a different LDR. Look for one with the lowest possible ON resistance. The GL5516 goes down to 300R-ish, so that's a good target. This will get you the subtle optical style with longer sustain - working as intended. If you want ridiculous chicken-pickin', try a superbright LED. The sustain knob will be pretty much useless and the sustain isn't right, but it will give that crazy squish attack. It sounded 'broken' but I had a fun afternoon with it like that.