I think it will be a lot like GTA in terms of gameplay.
Large open world with different missions to choose from at any time. Gunplay should be the same, but I think they are imrpoving it (tuning it would be more like it)
Honestly, I love GTA (I even loved GTA 4) so I cant wait for this game.
Check the first 2 gameplay videos on the opening post of the thread. That should give you an idea.