It's pretty fun. Multiplayer free roam is a blast when there are other players around. Love the gameplay, and it seems they took some of more annoying things out of GTA for this one (boring traveling across the map so far).
So is it like GTA, where you can just wander around killing people and stuff if you want, and then approach people to launch missions when you're good and ready?
Correct.
A few changes:
You can get an item called "campsite", which allows you to save anywhere in the wilderness, rather than having to go back to a safe house.
Your health regenerates, rather than having to eat food or sleep, to regain health.
Quick travel is available, kind of like taxi's, but faster and less expensive.
You can hunt and kill animals and skin them.
Rockstar social club integration, which adds further challenges and bonuses to the game.