I'm actually playing it currently. And I'm personally not particularly opposed to Ubisoft Game in all its forms; I'm not averse to collecting lots of icons from a map. In that light:
There's some nice ideas at the heart of it, but the implementation of those ideas is boils down to 'press button to make thing happen'. Also, it goes too far, to an absurd degree. It's just plain daft when you're standing on a scissor lift next to the control panel, and yet supposedly you're hacking it to control it. The damn buttons are there!
Are you meant to be able to hack every CTOS server room without entering the restricted zone at all? I did that for one, and it was quite satisfying, but I wasn't clear if that was a one-off or if it was meant to be possible for all of them.
There's occasionally a discussion that crops up here and elsewhere about how people would like to see "An open world game where you can enter every building!", then other people point out that quite quickly you'd find that most of that is irrelevant. I think Watch_Dogs reflects that sentiment quite nicely in a different way: It sounds awesome on paper to see that every NPC has a few character traits you can inspect, which gives way to much less excitement after you've played for a bit and reached a stage remarkably early on (I've not yet finished Act I, but done a ton of side content) where you only care about the few NPCs who have things you can take advantage of, with all the rest being just flavour.
Aiden has an irritating lack of self-awareness, at least at the stage I've got to. If they're trying to create an underlying message about how having so much data out there invades your privacy, actively encouraging the protagonist to even more directly invade privacy and revel in the voyeurism seems a bit dumb. You can't criticise something and at the same time encourage it unless you handle it much better than Watch_Dogs has thus far. I had similar criticisms about Connor in AC3, how the tone of how he was handled in gameplay differed from the way the storyline seemed to want me to perceive him.
There's an odd lack of balance in the minigames' progression requirements; five of the six minigames can be fully-done (as far as the progression wheel is concerned, at least) in just a few sessions, whereas to fully complete the drinking minigame takes thirty sessions, that can get quite long. And it's not even particularly difficult! I only failed it twice, and once was through not realising that going to the system menu didn't pause it, the other was having a sudden mental block about what some of the nomenclature meant. That drags on, and it's irritating because I was quite pleased at how non-demanding the other minigame progression requirements were.
The core idea of the real-world puzzle-solving - figuring out how to get line-of-sight on the things you want to hack - is actually rather good, although there's some odd inconsistencies: Why can I hack a switchbox from a camera when I can't hack it from being closer than that camera is? I do rather like that QR code challenges, too, although the various forms of "Follow this electrical line to get to a switchbox to open this device" got rather tedious rather quickly.
I accept that Aiden isn't an Assassin, but still, his parkour's a little weirdly dumb. If a gantry is just a few feet away from a rooftop I'd expect him to be able to make that jump, not leap over the railing to his death. Stealth movement is a bit fiddly, too. I feel like I'm meant to be exploring stealth options for the most part (the gunplay is a bit weedy, which seems odd when they've bothered to implement so many weapons) but it's all too easy to have Aiden decide to dive in a direction I wasn't trying to convey.
I love the idea of stealth driving, but think the current implementation is a little too unwieldy. And while we're on the subject of driving, taking out other cars (most notably in the convoys) starts out a bit too hard, with too few offensive options, and after unlocking a few abilities becomes far too easy, with too many offensive options. A middle ground would be nice.
The multiplayer invasion stuff is a nice idea, but a bit limited. That might partially be down to the opposition I've come up against, though. If I can stand on top of a car and shotgun an aggressor in the face, they may perhaps be better off using more refined tactics!
Clara bothers me. I quite like her personality - at least, what I've seen of it so far, but her character design is a bit too much "Let's make someone who looks as relentlessly countercultural as possible". It feels a little bit like some executive's idea of trendiness.
Oh, and a petty final thing: whoever signed off on distinguishing between two actions on a target as being "Take Down" and "Knock Down" deserves some harsh words. When viewing one in isolation is not sufficient to immediately know if you're allowed to kill or not without a little thought, you've goofed.
So, in short: It's much like recent Assassin's Creed. I don't particularly dislike it, irritants aside (and there's a lot of irritants this time around) but it doesn't particularly get my heart racing in any way. It's bland, which given how much potential the premise has, is something of a disappointment.