Announced for Spring 2013, but delayed to September 17th 2013. I don't mind waiting a few more months if it means quality. Because Rockstar takes their time with their games and they come out well, instead of rushing them for a quick buck.
I hope GTA 5 is a combination of San Andreas and GTAIV
It should borrow from San Andreas and re-implement these things:
The diverse environments, the thematic atmosphere, the diverse amount of things to do, a large amount of side content, character customization and a bit of surrealness
It should also continue in the direction that GTA IV pursued:
great characters, story-driven, plot choices, the usage of the cell phone, checkpoints, refined combat, a sense of realism, improving the physics, etc.