UPDATE 2.30pm: Ubisoft has deployed a patch for the game's online modes - which are currently, er, offline.
The update is not yet live however - it's been passed to Microsoft and Sony for certification, a process which can take some time. This means it will almost certainly miss tomorrow's launch date.
Here's Ubisoft's statement in full:
During the pre-launch phase of Watch Dogs 2, we discovered an issue tied to the seamless multiplayer feature that caused the game to lag and crash periodically. In order to eliminate that issue at launch and for players to enjoy a smooth game play experience, we have decided to wait to launch the seamless multiplayer feature until the patch that fixes this issue is deployed. The patch is currently in certification by Sony and Xbox.
In the meantime, players can still play the full single-player experience without any concerns and play co-op by inviting friends through the game menu. But that does mean that the Bounty-Hunter mode and other activities that would occur with other outside players who enter your game will be unavailable until the patch is deployed on each platform.
To follow updates on Watch Dogs 2 and follow the status of the seamless multiplayer, please feel free to visit our Watch Dogs 2 Community site.
Full details on exactly what is and isn't working lie below:
ORIGINAL STORY 11.00am: Watch Dogs 2 does not launch until tomorrow, but early copies are already in many players' hands and the game's review embargo has just lifted. However, Ubisoft's big new open-world is only part open for business.
As we reported over the weekend, Ubisoft has disabled Watch Dogs 2's "seamless multiplayer feature" until further notice because it "caused the game to lag and crash periodically".
Ubisoft is aware and told Eurogamer on Saturday it was confident the situation would be resolved by tomorrow for launch.
Eurogamer has consequently delayed publishing our Watch Dogs 2 review as a result.
In my experience, any attempt to play with other people left the game chugging at around 10fps until I quit and restarted - although the frequency this occurred varied among the Eurogamer team.
But while Ubisoft describes the issue as affecting the game's seamless online only - where players can suddenly appear in your game to hack or help you - the game's multiplayer servers are more affected than you might think.
Co-op gameplay does work - this is where you send a direct request to a friend to join you and you can play together. We tested this just now.
Online sessions with random co-op partners do not work - these are the purple icons on your map, for activity types such as taking over gang hideouts, freeing DedSec prisoners and the like.
You'll first see a message that Ubisoft servers are searching for other players nearby, then in your region, then finally globally. And then it will fail to connect.
These purple icon missions are suggested to the player frequently in the game's early stages and are a good source of XP. You can, however, go them alone (it's not too difficult to lone wolf them in my experience) - although this is hardly the point.
Finally, as Ubisoft states, seamless multiplayer does not work. This means the classic Watch Dogs invasion gameplay is currently unavailable - which is a big part of the game's fun.
That said, and now the review embargo has expired, I've really enjoyed the game's opening 10 hours or so. It's a hugely changed experience in tone and character from Watch Dogs 1 and there's a wealth of genuinely fun stuff to find and explore - such as hacking Ubisoft San Francisco for that unannounced Ubisoft sci-fi game trailer.
All of that will be soured, however, if the publisher cannot re-enable the game's suite of multiplayer modes soon.