What it'll be like? Alright, most of this information is half remembered details from a few weeks ago when I got the magazine.
From what I understand this is the first game the developer has truly allowed themselves free license with, previous games often had general directives issued by the publishers that restricted what they were able to do. The developer has an extensive knowledge of what they're going for in this game from past titles too, apparently.
In terms of storyline, you're a rogue royal assassin who has been framed for a murder. You don't like this, so your goal, is either to get revenge or clear your name, depending on your decisions within the game. If you're a brute, a murderer, it'll increase chaos, and you'll get the revenge ending, and if you're stealthy and discreet you'll increase order and get the justification ending, or something to that effect.
You've seen the art most likely so I probably don't have to detail that, but it has been described as steampunk. The entire world it is set in is very different to our own.
Gameplay-wise it is described as a set of interacting systems. Very difficult to explain properly. To give perspective a lot of games have a set of things you can and can't do. This game only has things you CAN do, within the scope of the game, if that makes sense. So, you have a possession power. It is useless to possess the fish, and most games wouldn't let you do it because of it, but this game does, because it is a set of interactive systems, if that makes any sense.
Because of this it allows for a lot of creativity with your myriad powers. An example already provided before on this forum, and in the magazine OXM, was that you are capable of summoning a colony of rats, attach a bomb to one of them and then possess the rat, effectively creating a controllable bomb. Of course this worries me, as I wonder how they will scale the AI so that it wont be too difficult or too easy. You have a lot of things to account for with a player who is capable of so much.
Speaking of your powers, of what I remember, including the rat colony and possession, you are capable of blinking, which is the ability to teleport a small distance in front of you. Could be very useful if you use it right. I can't remember any of the others but I'm pretty certain you can do other stuff. Mix that in with a melee combat system and the stealth and you've got a promising game. Dunno how you move about though. I'm guessing it'll be somewhat like Assassin's Creed.
That's pretty much everything I remember atm. If I brush up on my knowledge of it I'll update this.