This trailer in one word?
BWAAAAAAAAAAAAAAHH!
At first I was skeptical about the seeing through walls, shit, but now they've explained it a little more I'm kind of warming up to the concept. The disguise thing is a good idea as that was one part that I never really felt was all too solid in the other games. Being able to see through walls is a little redundant, but okay for gamers who aren't familiar with the series and I guess if the AI is going to be a little less predictable it does take some of that trial-and-error frustration out that some gamers found annoying about the series.
I preferred the frustration, to be honest. I love sitting down and staring at the map, watching the patterns of the enemies and waiting for just that right moment. I liked trying my hardest to get that perfect Assassin run by only bringing in the default weapons (fiber wire, syringes and explosives) as I felt the guns were pretty much useless since it's entirely possible to take out everyone with just those three items and whatever you found around the level.
The trial-and-error was fun because it meant that I could rethink my strategy and try to come up with the most efficient method of taking down my target, so it was really satisfying when I cleared a level without being detected, it also added to the tension of following someone and hoping that they don't turn around while you sneak up behind them, which kind of gave it a slightly retro difficulty, which I enjoyed.
Still, this doesn't look too bad, they're left it open enough for old-school Hitman players to do what they like and they've made it a little more versatile and forgiving for players who aren't used to that kind of difficulty. I say, if you don't like the new features, don't use them, they're not forcing you to.