I'm anxious to know what the time period will be, How it will be connected to the others, and if you will be able to create your own character. Though I think in the GTA world it adds to the story when you're playing a character that has a back story.
It could be set in London in the '60s, where the expansions for GTA 1 took place. London is the only city from the original 2D games that hasn't been reproduced in 3D. I'd really like to see a funky '70s version, though, since they've already covered the '60s, '80s and '90s.