Mixed opinions, but generally positive.
I have mixed feelings as regards Watch Dogs, but I generally liked it.
I never found the city of Chicago bland, as some have complained. I found the driving challenging at first, especially on a keyboard, but then I discovered that the key to successful driving was NOT to hold full accelerator at all times, and to be a little conservative with the turning.
I seldom felt pressured to do things any given, specific way; Aiden Pearce is an acceptably combat-effective protagonist to do things the militaristic way, but the hacking power gives him the ability to force multiply extremely effectively. It's much easier to unload an automatic shotgun in someone's face if they're bent over in agony from the screeching over their overloaded comms system, for instance.
Aiden does feel a little bland, but in retrospect, I believe that's largely because of the color of his allies, who are vibrant and very, very engaging.
I found the story to be good, overall, and very, very Film Noir-ish. I won't spoil it, but I will say that if you're familiar at all with the genre, it's going to feel similar.
My main problem was with the multiplayer. Specifically, the fact that a *lot* of content of single-player relevance (such as weapon pack unlocks, but most especially the notoriety-granted rewards,) are predicated upon multiplayer, and especially the Notoriety rewards, which are predicated upon a meter which only goes up if you are successful, and which actually goes DOWN if you're unsuccessful.
This is extremely problematic, and very, very poorly designed, especially as PC players quickly realized that if they were about to lose (and thus, watch their hard-earned Notoriety flush down the drain,) they could hit alt-F4 and make the game treat it as a disconnect, thus preventing them from losing any Notoriety (and in the process, preventing their almost-victorious opponent from gaining any.) Presumably console players could do the same by resetting, power-cycling, or pulling the Ethernet cable from their console, and once you realize this, the temptation to abort any losing multiplayer battle becomes almost impossible to resist.
Ultimately, the worst part about multiplayer invasions is that it quite simply is not what was promised. When Watch Dogs was hyped, it was promised that you could encounter other players just by strolling around, and you could choose to ignore them and let them go about their business, screw with them (if they allowed you to screw with them,) or actually decide to actively aid them, such as by providing covering fire if they were under attack. Ultimately, the only vestiges remaining of this are in Decryption and Online Free-Roam, which are quite simply not that fulfilling, especially Free-Roam, as there's literally nothing to do except start a huge gun-battle with the police, or troll other players by blowing up their cars, and hence the novelty soon wears off.