
GTA I

Sometimes when someone was running and you killed them or if their body flew back, a trail of blood would lead to their body. After a few seconds a pool of blood would appear under them.
Blood only got on the ground.

GTA II

When you hit people, blood particles would fly into the air but would disappear quickly. No blood got on the ground, at least on the PC version I used.
When you shot someone blood particles came out of the person and shot in one direction close together.

GTA III

Blood was able to get on the ground or on some flat horizontal surfaces. It looked different than previous games and blood particles flew out of people again when you shot them.
A little puddle of blood could get on the ground. Pools of blood formed under people again.
You could make bloody footprints for a short time if you walked through blood. Decapitations were possible.

GTA: Vice City

Basically the same as in III. Decapitations were possible again.

GTA: San Andreas

Again, basically the same as in the last two games.

GTAIV

The blood in IV was much more realistic than the previous games. Blood got on the screen if someone was shot close enough. It was able to splatter onto walls and cars.
There was a mist of blood mixed in with blood particles similar to previous games, though less noticeable. Pools of blood returned. No decapitations.
If you were shot a lot there would be blood on your clothes.

If someone was shot through a windshield, there would be a hole and then blood on the inside. If you hit someone then there would be a chance of getting blood on your car.

GTAV

The blood in V will act the same as in IV, with splattering on walls and such.

There will be enter and exit wounds.

It looks like there will be more variety in how blood looks depending on the attack.

Splatters are looking good so far.