I dont know why Crytek is reducing the killtimes, but its annoying. In the demo you had the perfect damage/armor. Now you get two shots from assault rifle and youre instant dead. I mean, we have a nano-suit, dont we?

Even the armor-mode is useless against this issue. When you played the demo, you had normal health, less health when cloaked, and more health when you were in armor-mode. But you were still fair armored with the mode so you could get killed by some more shots fired on you.
Now you have in armor-mode the same health as you had stealthmode in the demo. I felt about the killtimes exactly perfect between killtimes of my favorite games: Halo(which was too much) and CoD(which was too low). But now it seems like its the same health like CoD...

Why is Crytek changing so much? The demo was perfect like it was.

I assume that the long kill times were disadvantageous due to the ever-present lag issues. Shorter ones cut down on this and make the gameplay a little faster-paced. Personally, I like shorter kill times.

And, technically speaking, the nanosuit isn't really bulletproof without armor mode on, so in other modes it makes sense for quick death. Besides, is it really that annoying that you can take 15x the damage a normal human can take anyhow?

An ordinary human will be on the ground screaming from a shot in the leg, totally incapacitated from a shot to the stomach, unable to effectively use a weapon from a shot in the arm, and instantly dead from a shot in the head. So, yes, your nanosuit really is protecting you.