it's the detail... for example, it's not just whether or not to add vibrato, it's whether the vibrato is narrow or wide, fast or slow, whether you bend the note a bit sharp or flat sometimes. Maybe slur across frets rather than using vibrato, maybe mute a bit and so on....

I've followed the advice of many other players - limit yourself to a few notes, and then play them as many different ways as you can. By restricting the vocabulary, you have to be more creative with it's use. If you can do this for long enough, you'll find some of the stuff you did makes it's way in to your normal playing rather than being an exercise.

Some of the emotion comes from choice of mode as well - it's hard to make Lydian sound particularly dark, for example.....