PROS:
Open-world free roaming game.
Character clothing customization.
Many different missions.
Decent sized weapon and vehicle variety. (boats, helicopter, motorcycles, trucks). No planes.
Can shoot while driving, can steal any car.
Very good voice acting and believable characters.
Good story
A.I is actually decent, (perhaps other than cab drivers xD)
Multiplayer modes.
Decent cover mechanics for shooting.
Cons:
No planes. That's about it, maybe weapon variety could have been a bit better.
Sometimes missions may get a little repetitive.
One of the best games for its day, and can be a fresh experience with the addition of mods. Nothing else needs to be said. If you want the GTA experience, that's all here.