So much expression is available from your finger tips. Came across this great summary:

Pick Shape
Rounder Striking Area
More overtone damping
Warmer, deeper sound

More Pointed Shape
Less dampening of high frequency overtones
More precise note definition with faster response

Striking Surface
Smooth Edge Profile
Less overtone dampening
More precise note definition with faster response

Roughened/Worn Surface
More overtone dampening
Darker sound
More resistance and additional pick noise
Extra sonic space in front of a note

Rigidity
Thin/Flexible
Absorbs energy;even’s out the player’s attack
Consistent response for rhythmic playing

Thicker/Stiffer
Faster articulation
Greater dynamic range

Pick Location (Taken from this research paper)

When plucking close to the middle of the string, the amplitude of the fundamental tone is dominant, producing a clean, sine-like tone. When plucking closer to the edge of the string, more of the potential energy released goes into higher-pitch harmonic tones, producing a sharper sound.

Most of these ideas on come from a publication by Taylor Guitars. Much of this magic was lost about in some past robotic guitars.