If you watched the PS4 event in February, you already saw all most of the gameplay that was shown at the PAX East Watch_Dogs showing. It was the exact same gameplay, just shown from a different perspective. It looked impressive, but so did that video during the PS4 showing.
What was shown on top of the gameplay was interesting, though. It was said that the multiplayer aspect will be playable from other devices, including your smartphone. You will be able to take control of video cameras in the world and view your surroundings.
Also mentioned, was Aiden Pearce, the protagonist, who has access to the entirety of the “ctOS”, the city security system for a futuristic Chicago. Having access to the security allows him to intervene in random events (a la Red Dead Redemption), he can see the events of the people happening around him and it allows him the opportunity to do a good deed or two.
Overall, I would say I am very interested in what Watch_Dogs has to offer to the player. It seems to be a unique take on the open-world action genre. If Ubisoft can pull it off, Watch Dogs will be another game that could make an argument for a game of the year award this year. At this point there is still no solid release date, but late 2013 is expected.