The official GTA V online gameplay video is here;
Edit: Holy f*ck, the online MP is a whole different experience compared to previous parts;, from doing heists in coop, earning stuff to buy buildings and garages, hang out at your own place with friends, play the minigames (golf/teniis etc) with them, and it will have an editor too where you can create your own races and deathmatch games. This video you'll need to watch!
Actually the multiplayer (GTA V Online) won't be available untill 2 weeks after launch, but it basicly will be a sort of Persistant RPG Version of the GTA V singleplayer with 16 player instances, with all it's features present. I must admit I didn't expect MP to be this promising...
[video=youtube;olEGtoYs_8A]http://www.youtube.com/watch?v=olEGtoYs_8A[/video]
Here's some previews to read as well about the online part;
http://www.gamespot.com/features/why-grand-theft-auto-online-is-crazy-enough-to-work-6412714/?page=1
http://www.computerandvideogames.com/424264/gta-online-first-look-rockstars-persistent-online-world-is-its-most-ambitious-project-in-years/