I'm personally about 20hrs into the game now and still, finding the game fun and interesting whether I'm just walking around Chicago hacking people, checking out personal messages or spying on people. I got this game for free as part of Nvidia GTX sale so it is a good test of my new GTX 660 - whilst the game players more or less fine on Medium settings, it still doesn't run perfectly with occasional frame skips here and there, especially when driving - this is in part due to Ubisofts poor PC optimization of Watch_Dogs, so spec wise - it is fairly high.
The missions themselves are fairly straight-forward, the norm here - chase bad guys...race bad guys...spy on bad guys....the more annoying missions involve stealth which is where one of the issues appears, the cover system in WD isn't very good, in most cases its downright broken - imagine your trying to circumvent many gangsters using the cover system, you want to move from point 'A to B', simple enough right? However, more than often - it'll take you to 'C' because your targeting reticule wasn't perfectly aligned, or the game thinks your character is better off moving to C rather than B. Or other cases, where you want to hack an object, and something else happens like exploding a transformer...weird stuff like that happens all too often.
Graphic wise, its very good - highly detailed even on medium settings. I am using Worsemod though which does improve textures but still, from eye candy point of view, Watch_Dogs is quite pleasing to the eye.
Combat can get tricky sometimes, as changing weapons feels clunky and unresponsive - even using hacks or blocking people from calling for help - can get tricky too but overall, its acceptable most of the time. I'd like to see more personalization of the main character, the clothing store just sells re-skins which is a missed opportunity.
Overall, Watch_Dogs is a fun open world game - it has a lot to offer players. Probably would be better off without the forced uPlay DRM though.