Facial features are more prominent
Characters in the original games had blurry and unclear faces. Many features of the face were missed due to the blur, and players could never really figure out the true face of the characters.
In GTA The Trilogy Definitive Edition, Rockstar Games has made each character's face extremely clear and readable. It will be more fun playing the games now because players get an exact representation of all the characters they interact with.
many games are taking light sources in the game into heavy consideration.