I have played the Xbox 360 version for about 90 mins so far and I would like to give my quick opinion.
First of all, if you get the 360 version do not install the 2nd disc. I installed the 2nd disc to a flash drive just like GTAV and had nothing but issues. Put disc 1 in, let it install through the game menu and play off disc 2.
First the graphics. The Xbox 360 just turned 9 years old and it really shows in Watchdogs. LOD is really bad. Framerate is not stable when there is much action on screen. Everything looks blurry and low res. It looks a lot like GTAV on 360 to me.
The actual gameplay is good though. During the first mission I died a couple times trying to brute force my way through. It seems at least early on you will not be able to easily gun your way through the game, you die pretty quick and the enemies are quick to shoot. You can also get shot while you are hacking during minigames so you really have to hide if you are going to be hacking systems.
If you are familiar with Farcry3 then you already have a good idea about the open world activities. There are data centers around the city you need to hack into for control, and cell towers you need to climb and hack to get more objectives and mini games. Instead of hunting you need to hack people or go to pawn shop to get components to craft the bigger hacks in the game.
The map is absolutely huge. It would take at least 4-5 screenshots to capture the entire map when zoomed out all the way. I like the atmosphere of the game and it will keep you very busy, you cant walk more then 10 feet without a sidequest showing up.
Im getting the PS4 version on Tuesday and will probably wait until then to play more. The little I played made me more excited about the game.