I've been playing this game since day 1 when it came out, for 4 days straight, everyday for aprox 18 hours. In less than 3 days I finished the main missions and most of the optional side missions (game completion at 75%), without stealing more than 3 cars/vehicles in total (in the stats I have Trevor with one police car stolen and Michael with one FireTruck and a Taxi stolen, Franklin didn't steal no nothing). I also played on the side Online in that game time and reached a Rank over 20, it's great fun with or without friends.

It feels like this game is a drug that stole my life...but I don't regret a thing.

Things I really enjoyed and you should probably do too:
The game, despite it's large size, it's amazingly optimized with many graphic options to tweak. I have exactly the minimum requirements and I can run it, sure I had to turn every fancy pc enchanting option off and it looks like the graphics on the old-gen consoles, but I am happy, it works with +30fps.

The missions are really captivating, the money spending system feels more challenging (because you have a lot to spend it on, to invest it, to simly lose it). You get to meet many interesting sidecharacters and the overall voiceacting is really good. Besides the actual story and the many twists in the missions, they have quite a replay value due to their minichallenges for each of them (like 'finish in the required time', 'complete it in a certain order' etc.) if you are a completionist.

The car handleing, amazing, the gave up the GTA IV 'simulator' like driving and brought back the arcade like car handling from the older ones, where you can rotate in the air or do some nice stunts.

The world is really immersing, each NPC with it's small story, with their interactions etc. It's a living world filled with living people, animals and moments...and with Internet, Radio and Cable TV!

I can't quite say there is a lot of choice based tasks, but there is a really decent number of those, most of them involving planning or the interaction choice, but as long as you have imagination there will always be a choice.

It's great that we have animals, you can kill them, you can play/interact with them, you can even become them at a certain point (hidden easter egg). Most of the people are avereage aged, from 20-60 or so, I kinda wished we also had the extrems like children or quite old people...sure it would probablly create some controversy, but it would make give the game an even more real feeling.

And I could enumerate so many more...but now I have to get back to the game.