I do get the feeling this might be a slight remake of Vice City/GTA III with the voice-over. GTA F News Blog even mentions that the main character could be Tommy Vercetti. Keep in mind the GTA 4 series started another universe/timeline from the GTA III series of games.
And, this seems to be a different version of Los Santos. There are tons of rumors running around about the upcoming game too.
Keep in mind GTA 4 had early trailers that had different aspects in the trailer, which weren’t in the final game.
Another main character? Some people believe there will be different main characters to play as in the game.