What's it like? Would you recommend it for someone who played oblivion and liked it.
It's not really anything like Oblivion, aside from being first person and having melee and magic. Dishonored is an immersive sim in the tradition of Thief and Deus Ex, but set in a steampunk(ish) world. It's not open world, but the levels will offer a large degree of freedom. You can choose stealth, melee, magic or any combination of them to get through.
It's being made by Arkane, who did Dark Messiah of Might and Magic and Arx Fatalis, with the addition of Harvey Smith, who was the lead designer of Deus Ex. If that sounds like a nice combination to you, you'll probably like it.