What I miss from previous GTA's, is that you can no longer stand in the open to shoot at enemies. In III, VC SA, you could easily stand in the open (you do it in pretty much every mission) and mow down emenies with Minigun/M4, because there's no cover system. In IV and V, there's a cover system, and if you stand out in the open you wil get killed fast, because the protoganists are weaker, and R* maybe did it to stimulate the use of the cover system.
It annoys me, because if you can't find a good cover spot quick enough, you're f*cked. This is especially true for Online.