[Arcanum]

Looks open world sandbox from the minimap and the various scenes in the opening moments of the trailer.

As for the hacking you've got Bridges, Traffic Lights, Jam Communications, Control Train, and then what I'm guessing is Control Car and detonating a gas line or something (plus those two blank slots, which could be abilities either not yet in the game, or obtained at a future point in the story). In keeping with the open world sandbox impression, it seems logical that you could use these abilities whenever you want, so long as there's a viable target nearby.

If they're taking some influence from Assassin's Creed, then there's more than one way to kill a guy. There were no indications that you had to beat up that one security guard and intercept Demarco before he even got out of his car. It could be possible to wait inside the club and take him out there. Likewise there was no indication to jam communications so that you could enter the club. And we know there was a back door, so maybe you could have snuck in that way.

Obviously this is all speculation, but I was getting some heavy AC vibes from the game, and not Splinter Cell or Heavy Rain (I actually have no idea why you're comparing this game to Heavy Rain :S).

e- On the traffic lights, it looks like they recognized and locked onto the waypoint/objective/target, which means one of two things. 1) the hacking is limited to plot only, which is stupid, limiting, and if it's a sandbox game then ubisoft is taking some huge steps backwards from AC, so this seems unlikely. 2) The lock-on is to facilitate the timing, possibly taking the exact moment of activation out of your hands so that it guarantees the lights are hacked at the right time, which would allow any player to pull off a stunt like in the demonstration. My money's on option 2.