I've played the PS4 version for about 2 hours so here it goes.
First off the big issue, the graphics.....are good. Not great. Not horrible. As a lot of other people have said, the game looks it's best during night and when it's raining. But the character models are still decent and I thought the animations for everything were really well done. Is it the next gen graphics everybody wanted from two e3s ago? No, but they are still decent and I think the next in the series could benefit by being developed for current gen only.
The realism is top notch and matches GTA levels of immersion IMO. As you've probably seen, every person you walk by has a backstory and some info, you can't hack everybody but just a few people very now and then. The engine can push a lot of objects on screen at one time. I caused a wreck in downtown using the traffic light hack, in the initial pileup was probably 5 cars but once you looked past the wreck there were more than 20 cars backed up at a standstill waiting on the wreck with plenty of people still walking around the streets.
The missions so far have been fairly average, nothing sticks out as revolutionary or different from your typical open world games like GTA, AC, etc. but I am only 2 hours in so we will see if that changes. I do like that they do have stealth mechanics in this game, it allows you to quietly hack and stealth kill guys or just go in guns blazing to get to your objective.
The last thing that I'll note is it's insanely hard to get away from the cops right now. When being chased, you almost have to use some hack to get them to crash and lose your tail. They drive faster than you, take corners perfectly while barely slowing down, and are incredibly aggressive. Once you finally lose them, they call for backup and the ctos system begins scanning for you, represented by green circles that randomly show up on your minimap. These are hard to avoid because they are fairly big, there's a lot of them, and sometimes they move before fading away. Stay in a green circle for too long and the system locates you again and the cops are back on your tail.
My multiplayer is set to on, but I've yet to be invaded or go into somebody else's game so I can't comment on that.
For the TLDR crowd: a pretty good game that's definitely fun but has some frustrating aspects to it and could still use a little polish. It's not GTA perfect but that doesn't make it a bad game. It's not game of the year but I'd give it an 8 to an 8.5 out of 10.