This is by far the biggest achievement of Rockstar North's development history and a milestone of the current generation
But, the game is the most immersive game I have played in the last few years. Three cities, each with a distinct theme and miles upon miles of wilderness, desert and small towns to run around in. There is never a shortage of things to do and getting from one area to another is simply a fun experience. The story and side missions are varied and none are ridiculously difficult (except for Supply Lines, though I heard later versions eased the difficulty). Epic missions like driving a motorcycle down a runway into a moving cargo plane will thrill you and tolerable stealth missions change things up a bit. Simple amazing the missions are.
The aiming system has finally achived perfection with Rockstar North getting hints from Manhunt. They adopted the entire targeting system from that game and is works like a charm. I was honestly disappointed when Liberty City Stories didn't use it because it fixed the broken aiming system which plagued GTA3 and VC.
The music personifies the early '90s when West Coast Hip-Hop was on the rise and grunge music was in and both are represented (though the kings of that genre, Nirvana, are completely absent due to probably legal problems). Listening to the radio in GTA while driving around listening to music and the radio hosts is a experience that I won't find in any other GTA title.
The script is by far the most hilarious thing I've heard with the conversations between Catalina and CJ sending me to tears. The cutscenes are witty, sharp and entertaining. Sure the plot doesn't really inspire greatness but the writing alone makes it tolerable (though Tenpenny and his cop buddies are some sinister villains).
If you play this: go for 100% completion as it will guarentee you the entire GTA experience. Playing the missions isn't enough, immerse yourself in this world and you will be rewarded.