I'm really enjoying this game, was up until 3 AM messing about with it. If you like stealth gameplay, it has some interesting twists. Nothing earth-shattering but just cool to play around with.
For instance, you don't get magical 'eagle vision' or 'hitman'instinct' but hack into static and wearable cameras to scope out a place. Hopping for camera to camera is an interesting mechanic and you can set off distractions and traps in this mode.
I also have fun using car stealth to escape police dragnets and actually have more success with it than trying to barrel through the town with screaming sirens behind me. You can hide under bridges from police helicopters, park in garages to let patrol cars pass and even kill the engine and hide under the dash while the cops shine flashlights over you. If it comes together (meaning no AI glitch or instant-fail campaign missions) you'll feel like Ryan Gosling in the opening scene of Driver.
The gunplay is best when you're prepared so you can use environmental traps and cover to your best advantage. When you lose the initiative, it often escalates so fast you barely have time to respond tactically and you're forced to be cover-hugging Rambo while enemies swarm over you. I enjoy it most when setting an ambush for a criminal convoy (if you've seen the excellent movie Ronin, imagine that.) It's at its worst when you fail a stealth run halfway through and the response is unrealistically brutal.
The big sticking point for me is the main character. Not only is he walking videogame cliche to the point of satire (white unshaven man with a glare and a whiskey voice), he acts like an absolute douche throughout and wears the dorkiest designer clothes imaginable, like an anime character magically transported to the gritty real world. Worse than that, he's a prototypical nerd fantasy: super hacker, super ninja, super athelete, super driver, proficient in all firearms, tortured by his past, a lone wolf who is nonethless admired by all he crosses paths with, just ugh.
This game is easy to nitpick and there are rough edges as people have pointed out in this thread. But when everything comes together, it's a blast.